diff --git a/src/Executor/Values.php b/src/Executor/Values.php
index 2e12ce0..ef33c5a 100644
--- a/src/Executor/Values.php
+++ b/src/Executor/Values.php
@@ -94,7 +94,7 @@ class Values
      * @return array
      * @throws Error
      */
-    public static function getArgumentValues($def, $node, $variableValues)
+    public static function getArgumentValues($def, $node, $variableValues = null)
     {
         $argDefs = $def->args;
         $argNodes = $node->arguments;
diff --git a/src/Type/Definition/Directive.php b/src/Type/Definition/Directive.php
index dda85c7..f1c8c55 100644
--- a/src/Type/Definition/Directive.php
+++ b/src/Type/Definition/Directive.php
@@ -107,7 +107,7 @@ class Directive
                         new FieldArgument([
                             'name' => 'if',
                             'type' => Type::nonNull(Type::boolean()),
-                            'description' => 'Skipped when true'
+                            'description' => 'Skipped when true.'
                         ])
                     ]
                 ]),
diff --git a/src/Type/Introspection.php b/src/Type/Introspection.php
index 2a8db04..c8fa398 100644
--- a/src/Type/Introspection.php
+++ b/src/Type/Introspection.php
@@ -235,8 +235,8 @@ EOD;
                 'description' =>
                     'A GraphQL Schema defines the capabilities of a GraphQL ' .
                     'server. It exposes all available types and directives on ' .
-                    'the server, as well as the entry points for query and ' .
-                    'mutation operations.',
+                    'the server, as well as the entry points for query, mutation, and ' .
+                    'subscription operations.',
                 'fields' => [
                     'types' => [
                         'description' => 'A list of all types supported by this server.',
@@ -288,7 +288,7 @@ EOD;
                 'name' => '__Directive',
                 'description' =>     'A Directive provides a way to describe alternate runtime execution and ' .
                     'type validation behavior in a GraphQL document.' .
-                    '\n\nIn some cases, you need to provide options to alter GraphQL’s ' .
+                    "\n\nIn some cases, you need to provide options to alter GraphQL's " .
                     'execution behavior in ways field arguments will not suffice, such as ' .
                     'conditionally including or skipping a field. Directives provide this by ' .
                     'describing additional information to the executor.',
@@ -664,7 +664,7 @@ EOD;
         if (!isset(self::$map['__TypeKind'])) {
             self::$map['__TypeKind'] = new EnumType([
                 'name' => '__TypeKind',
-                'description' => 'An enum describing what kind of type a given __Type is.',
+                'description' => 'An enum describing what kind of type a given `__Type` is.',
                 'values' => [
                     'SCALAR' => [
                         'value' => TypeKind::SCALAR,
diff --git a/src/Utils.php b/src/Utils.php
index 7dae895..1507182 100644
--- a/src/Utils.php
+++ b/src/Utils.php
@@ -180,6 +180,14 @@ class Utils
         return $grouped;
     }
 
+    public static function keyValMap($traversable, callable $keyFn, callable $valFn)
+    {
+        return array_reduce($traversable, function ($map, $item) use ($keyFn, $valFn) {
+            $map[$keyFn($item)] = $valFn($item);
+            return $map;
+        }, []);
+    }
+
     /**
      * @param $traversable
      * @param callable $predicate
diff --git a/src/Utils/BuildSchema.php b/src/Utils/BuildSchema.php
new file mode 100644
index 0000000..718d61f
--- /dev/null
+++ b/src/Utils/BuildSchema.php
@@ -0,0 +1,530 @@
+<?php
+namespace GraphQL\Utils;
+
+use GraphQL\Error\Error;
+use GraphQL\Executor\Values;
+use GraphQL\Language\AST\DirectiveDefinitionNode;
+use GraphQL\Language\AST\DocumentNode;
+use GraphQL\Language\AST\EnumTypeDefinitionNode;
+use GraphQL\Language\AST\InputObjectTypeDefinitionNode;
+use GraphQL\Language\AST\InterfaceTypeDefinitionNode;
+use GraphQL\Language\AST\NodeKind;
+use GraphQL\Language\AST\ObjectTypeDefinitionNode;
+use GraphQL\Language\AST\ScalarTypeDefinitionNode;
+use GraphQL\Language\AST\TypeDefinitionNode;
+use GraphQL\Language\AST\TypeNode;
+use GraphQL\Language\AST\UnionTypeDefinitionNode;
+use GraphQL\Language\Parser;
+use GraphQL\Language\Token;
+use GraphQL\Schema;
+use GraphQL\Type\Definition\Directive;
+use GraphQL\Type\Definition\EnumType;
+use GraphQL\Type\Definition\InputObjectType;
+use GraphQL\Type\Definition\InterfaceType;
+use GraphQL\Type\Definition\FieldArgument;
+use GraphQL\Type\Definition\NonNull;
+use GraphQL\Type\Definition\ObjectType;
+use GraphQL\Type\Definition\CustomScalarType;
+use GraphQL\Type\Definition\Type;
+use GraphQL\Type\Definition\UnionType;
+use GraphQL\Type\Introspection;
+use GraphQL\Utils;
+
+/**
+ * Class BuildSchema
+ * @package GraphQL\Utils
+ */
+class BuildSchema
+{
+    /**
+     * @param Type $innerType
+     * @param TypeNode $inputTypeNode
+     * @return Type 
+     */
+    private function buildWrappedType(Type $innerType, TypeNode $inputTypeNode)
+    {
+        if ($inputTypeNode->kind == NodeKind::LIST_TYPE) {
+            return Type::listOf($this->buildWrappedType($innerType, $inputTypeNode->type));
+        }
+        if ($inputTypeNode->kind == NodeKind::NON_NULL_TYPE) {
+            $wrappedType = $this->buildWrappedType($innerType, $inputTypeNode->type);
+            Utils::invariant(!($wrappedType instanceof NonNull), 'No nesting nonnull.');
+            return Type::nonNull($wrappedType);
+        }
+        return $innerType;
+    }
+
+    private function getNamedTypeNode(TypeNode $typeNode)
+    {
+        $namedType = $typeNode;
+        while ($namedType->kind === NodeKind::LIST_TYPE || $namedType->kind === NodeKind::NON_NULL_TYPE) {
+            $namedType = $namedType->type;
+        }
+        return $namedType;
+    }
+
+    /**
+     * This takes the ast of a schema document produced by the parse function in
+     * GraphQL\Language\Parser.
+     *
+     * If no schema definition is provided, then it will look for types named Query
+     * and Mutation.
+     *
+     * Given that AST it constructs a GraphQLSchema. The resulting schema
+     * has no resolve methods, so execution will use default resolvers.
+     *
+     * @param DocumentNode $ast
+     * @return Schema
+     * @throws Error
+     */
+    public static function buildAST(DocumentNode $ast)
+    {
+        $builder = new self($ast);
+        return $builder->buildSchema();
+    }
+
+    private $ast;
+    private $innerTypeMap;
+    private $nodeMap;
+
+    public function __construct(DocumentNode $ast)
+    {
+        $this->ast = $ast;
+    }
+    
+    public function buildSchema()
+    {
+        $schemaDef = null;
+        $typeDefs = [];
+        $this->nodeMap = [];
+        $directiveDefs = [];
+        foreach ($this->ast->definitions as $d) {
+            switch ($d->kind) {
+                case NodeKind::SCHEMA_DEFINITION:
+                    if ($schemaDef) {
+                        throw new Error('Must provide only one schema definition.');
+                    }
+                    $schemaDef = $d;
+                    break;
+                case NodeKind::SCALAR_TYPE_DEFINITION:
+                case NodeKind::OBJECT_TYPE_DEFINITION:
+                case NodeKind::INTERFACE_TYPE_DEFINITION:
+                case NodeKind::ENUM_TYPE_DEFINITION:
+                case NodeKind::UNION_TYPE_DEFINITION:
+                case NodeKind::INPUT_OBJECT_TYPE_DEFINITION:
+                    $typeDefs[] = $d;
+                    $this->nodeMap[$d->name->value] = $d;
+                    break;
+                case NodeKind::DIRECTIVE_DEFINITION:
+                    $directiveDefs[] = $d;
+                    break;
+            }
+        }
+
+        $queryTypeName = null;
+        $mutationTypeName = null;
+        $subscriptionTypeName = null;
+        if ($schemaDef) {
+            foreach ($schemaDef->operationTypes as $operationType) {
+                $typeName = $operationType->type->name->value;
+                if ($operationType->operation === 'query') {
+                    if ($queryTypeName) {
+                        throw new Error('Must provide only one query type in schema.');
+                    }
+                    if (!isset($this->nodeMap[$typeName])) {
+                        throw new Error(
+                            'Specified query type "' . $typeName . '" not found in document.'
+                        );
+                    }
+                    $queryTypeName = $typeName;
+                } else if ($operationType->operation === 'mutation') {
+                    if ($mutationTypeName) {
+                        throw new Error('Must provide only one mutation type in schema.');
+                    }
+                    if (!isset($this->nodeMap[$typeName])) {
+                        throw new Error(
+                            'Specified mutation type "' . $typeName . '" not found in document.'
+                        );
+                    }
+                    $mutationTypeName = $typeName;
+                } else if ($operationType->operation === 'subscription') {
+                    if ($subscriptionTypeName) {
+                        throw new Error('Must provide only one subscription type in schema.');
+                    }
+                    if (!isset($this->nodeMap[$typeName])) {
+                        throw new Error(
+                            'Specified subscription type "' . $typeName . '" not found in document.'
+                        );
+                    }
+                    $subscriptionTypeName = $typeName;
+                }
+            }
+        } else {
+            if (isset($this->nodeMap['Query'])) {
+                $queryTypeName = 'Query';
+            }
+            if (isset($this->nodeMap['Mutation'])) {
+                $mutationTypeName = 'Mutation';
+            }
+            if (isset($this->nodeMap['Subscription'])) {
+                $subscriptionTypeName = 'Subscription';
+            }
+        }
+
+        if (!$queryTypeName) {
+            throw new Error(
+                'Must provide schema definition with query type or a type named Query.'
+            );
+        }
+
+        $this->innerTypeMap = [
+            'String' => Type::string(),
+            'Int' => Type::int(),
+            'Float' => Type::float(),
+            'Boolean' => Type::boolean(),
+            'ID' => Type::id(),
+            '__Schema' => Introspection::_schema(),
+            '__Directive' => Introspection::_directive(),
+            '__DirectiveLocation' => Introspection::_directiveLocation(),
+            '__Type' => Introspection::_type(),
+            '__Field' => Introspection::_field(),
+            '__InputValue' => Introspection::_inputValue(),
+            '__EnumValue' => Introspection::_enumValue(),
+            '__TypeKind' => Introspection::_typeKind(),
+        ];
+
+        $types = array_map(function($def) {
+            return $this->typeDefNamed($def->name->value);
+        }, $typeDefs);
+
+        $directives = array_map([$this, 'getDirective'], $directiveDefs);
+
+        // If specified directives were not explicitly declared, add them.
+        $skip = array_reduce($directives, function($hasSkip, $directive) {
+            return $hasSkip || $directive->name == 'skip';
+        });
+        if (!$skip) {
+            $directives[] = Directive::skipDirective();
+        }
+
+        $include = array_reduce($directives, function($hasInclude, $directive) {
+            return $hasInclude || $directive->name == 'include';
+        });
+        if (!$include) {
+            $directives[] = Directive::includeDirective();
+        }
+
+        $deprecated = array_reduce($directives, function($hasDeprecated, $directive) {
+            return $hasDeprecated || $directive->name == 'deprecated';
+        });
+        if (!$deprecated) {
+            $directives[] = Directive::deprecatedDirective();
+        }
+
+        return new Schema([
+            'query' => $this->getObjectType($this->nodeMap[$queryTypeName]),
+            'mutation' => $mutationTypeName ?
+                $this->getObjectType($this->nodeMap[$mutationTypeName]) :
+                null,
+            'subscription' => $subscriptionTypeName ?
+                $this->getObjectType($this->nodeMap[$subscriptionTypeName]) :
+                null,
+            'types' => $types,
+            'directives' => $directives,
+        ]);
+    }
+
+    private function getDirective(DirectiveDefinitionNode $directiveNode)
+    {
+        return new Directive([
+            'name' => $directiveNode->name->value,
+            'description' => $this->getDescription($directiveNode),
+            'locations' => array_map(function($node) {
+                return $node->value;
+            }, $directiveNode->locations),
+            'args' => $directiveNode->arguments ? FieldArgument::createMap($this->makeInputValues($directiveNode->arguments)) : null,
+        ]);
+    }
+
+    private function getObjectType(TypeDefinitionNode $typeNode)
+    {
+        $type = $this->typeDefNamed($typeNode->name->value);
+        Utils::invariant(
+            $type instanceof ObjectType,
+            'AST must provide object type.'
+        );
+        return $type;
+    }
+
+    private function produceType(TypeNode $typeNode)
+    {
+        $typeName = $this->getNamedTypeNode($typeNode)->name->value;
+        $typeDef = $this->typeDefNamed($typeName);
+        return $this->buildWrappedType($typeDef, $typeNode);
+    }
+
+    private function produceInputType(TypeNode $typeNode)
+    {
+        $type = $this->produceType($typeNode);
+        Utils::invariant(Type::isInputType($type), 'Expected Input type.');
+        return $type;
+    }
+
+    private function produceOutputType(TypeNode $typeNode)
+    {
+        $type = $this->produceType($typeNode);
+        Utils::invariant(Type::isOutputType($type), 'Expected Input type.');
+        return $type;
+    }
+
+    private function produceObjectType(TypeNode $typeNode)
+    {
+        $type = $this->produceType($typeNode);
+        Utils::invariant($type instanceof ObjectType, 'Expected Object type.');
+        return $type;
+    }
+
+    private function produceInterfaceType(TypeNode $typeNode)
+    {
+        $type = $this->produceType($typeNode);
+        Utils::invariant($type instanceof InterfaceType, 'Expected Input type.');
+        return $type;
+    }
+
+    private function typeDefNamed($typeName)
+    {
+        if (isset($this->innerTypeMap[$typeName])) {
+            return $this->innerTypeMap[$typeName];
+        }
+
+        if (!isset($this->nodeMap[$typeName])) {
+            throw new Error('Type "' . $typeName . '" not found in document.');
+        }
+
+        $innerTypeDef = $this->makeSchemaDef($this->nodeMap[$typeName]);
+        if (!$innerTypeDef) {
+            throw new Error("Nothing constructed for $typeName.");
+        }
+        $this->innerTypeMap[$typeName] = $innerTypeDef;
+        return $innerTypeDef;
+    }
+
+    private function makeSchemaDef($def)
+    {
+        if (!$def) {
+            throw new Error('def must be defined.');
+        }
+        switch ($def->kind) {
+            case NodeKind::OBJECT_TYPE_DEFINITION:
+                return $this->makeTypeDef($def);
+            case NodeKind::INTERFACE_TYPE_DEFINITION:
+                return $this->makeInterfaceDef($def);
+            case NodeKind::ENUM_TYPE_DEFINITION:
+                return $this->makeEnumDef($def);
+            case NodeKind::UNION_TYPE_DEFINITION:
+                return $this->makeUnionDef($def);
+            case NodeKind::SCALAR_TYPE_DEFINITION:
+                return $this->makeScalarDef($def);
+            case NodeKind::INPUT_OBJECT_TYPE_DEFINITION:
+                return $this->makeInputObjectDef($def);
+            default:
+                throw new Error("Type kind of {$def->kind} not supported.");
+        }
+    }
+
+    private function makeTypeDef(ObjectTypeDefinitionNode $def)
+    {
+        $typeName = $def->name->value;
+        return new ObjectType([
+            'name' => $typeName,
+            'description' => $this->getDescription($def),
+            'fields' => function() use ($def) { return $this->makeFieldDefMap($def); },
+            'interfaces' => function() use ($def) { return $this->makeImplementedInterfaces($def); }
+        ]);
+    }
+
+    private function makeFieldDefMap($def)
+    {
+        return Utils::keyValMap(
+            $def->fields,
+            function ($field) {
+                return $field->name->value;
+            },
+            function($field) {
+                return [
+                    'type' => $this->produceOutputType($field->type),
+                    'description' => $this->getDescription($field),
+                    'args' => $this->makeInputValues($field->arguments),
+                    'deprecationReason' => $this->getDeprecationReason($field->directives)
+                ];
+            }
+        );
+    }
+
+    private function makeImplementedInterfaces(ObjectTypeDefinitionNode $def)
+    {
+        return isset($def->interfaces) ? array_map([$this, 'produceInterfaceType'], $def->interfaces) : null;
+    }
+
+    private function makeInputValues($values)
+    {
+        return Utils::keyValMap(
+            $values,
+            function ($value) {
+                return $value->name->value;
+            },
+            function($value) {
+                $type = $this->produceInputType($value->type);
+                $config = [
+                    'name' => $value->name->value,
+                    'type' => $type,
+                    'description' => $this->getDescription($value)
+                ];
+                if (isset($value->defaultValue)) {
+                    $config['defaultValue'] = Utils\AST::valueFromAST($value->defaultValue, $type);
+                }
+                return $config;
+            }
+        );
+    }
+
+    private function makeInterfaceDef(InterfaceTypeDefinitionNode $def)
+    {
+        $typeName = $def->name->value;
+        return new InterfaceType([
+            'name' => $typeName,
+            'description' => $this->getDescription($def),
+            'fields' => function() use ($def) { return $this->makeFieldDefMap($def); },
+            'resolveType' => [$this, 'cannotExecuteSchema']
+        ]);
+    }
+
+    private function makeEnumDef(EnumTypeDefinitionNode $def)
+    {
+        return new EnumType([
+            'name' => $def->name->value,
+            'description' => $this->getDescription($def),
+            'values' => Utils::keyValMap(
+                $def->values,
+                function($enumValue) {
+                    return $enumValue->name->value;
+                },
+                function($enumValue) {
+                    return [
+                        'description' => $this->getDescription($enumValue),
+                        'deprecationReason' => $this->getDeprecationReason($enumValue->directives)
+                    ];
+                }
+            )
+        ]);
+    }
+
+    private function makeUnionDef(UnionTypeDefinitionNode $def)
+    {
+        return new UnionType([
+            'name' => $def->name->value,
+            'description' => $this->getDescription($def),
+            'types' => array_map([$this, 'produceObjectType'], $def->types),
+            'resolveType' => [$this, 'cannotExecuteSchema']
+        ]);
+    }
+
+    private function makeScalarDef(ScalarTypeDefinitionNode $def)
+    {
+        return new CustomScalarType([
+            'name' => $def->name->value,
+            'description' => $this->getDescription($def),
+            'serialize' => function() { return false; },
+            // Note: validation calls the parse functions to determine if a
+            // literal value is correct. Returning null would cause use of custom
+            // scalars to always fail validation. Returning false causes them to
+            // always pass validation.
+            'parseValue' => function() { return false; },
+            'parseLiteral' => function() { return false; }
+        ]);
+    }
+
+    private function makeInputObjectDef(InputObjectTypeDefinitionNode $def)
+    {
+        return new InputObjectType([
+            'name' => $def->name->value,
+            'description' => $this->getDescription($def),
+            'fields' => function() use ($def) { return $this->makeInputValues($def->fields); }
+        ]);
+    }
+
+    private function getDeprecationReason($directives)
+    {
+        $deprecatedAST = $directives ? Utils::find(
+            $directives,
+            function($directive) {
+                return $directive->name->value === Directive::deprecatedDirective()->name;
+            }
+        ) : null;
+        if (!$deprecatedAST) {
+            return;
+        }
+        return Values::getArgumentValues(
+            Directive::deprecatedDirective(),
+            $deprecatedAST
+        )['reason'];
+    }
+
+    /**
+     * Given an ast node, returns its string description based on a contiguous
+     * block full-line of comments preceding it.
+     */
+    public function getDescription($node)
+    {
+        $loc = $node->loc;
+        if (!$loc) {
+            return;
+        }
+        $comments = [];
+        $minSpaces = null;
+        $token = $loc->startToken->prev;
+        while (
+            $token &&
+            $token->kind === Token::COMMENT &&
+            $token->next && $token->prev &&
+            $token->line + 1 === $token->next->line &&
+            $token->line !== $token->prev->line
+        ) {
+            $value = $token->value;
+            $spaces = $this->leadingSpaces($value);
+            if ($minSpaces === null || $spaces < $minSpaces) {
+                $minSpaces = $spaces;
+            }
+            $comments[] = $value;
+            $token = $token->prev;
+        }
+        return implode("\n", array_map(function($comment) use ($minSpaces) {
+            return mb_substr(str_replace("\n", '', $comment), $minSpaces);
+        }, array_reverse($comments)));
+    }
+
+    /**
+     * A helper function to build a GraphQLSchema directly from a source
+     * document.
+     * 
+     * @param Source|string $source
+     * @return
+     */
+    public static function build($source)
+    {
+        return self::buildAST(Parser::parse($source));
+    }
+
+    // Count the number of spaces on the starting side of a string.
+    private function leadingSpaces($str)
+    {
+        return strlen($str) - strlen(ltrim($str));
+    }
+
+    public function cannotExecuteSchema() {
+        throw new Error(
+            'Generated Schema cannot use Interface or Union types for execution.'
+        );
+    }
+
+}
\ No newline at end of file
diff --git a/src/Utils/SchemaPrinter.php b/src/Utils/SchemaPrinter.php
new file mode 100644
index 0000000..91099d4
--- /dev/null
+++ b/src/Utils/SchemaPrinter.php
@@ -0,0 +1,304 @@
+<?php
+namespace GraphQL\Utils;
+
+use GraphQL\Language\Printer;
+use GraphQL\Schema;
+use GraphQL\Type\Definition\EnumType;
+use GraphQL\Type\Definition\InputObjectType;
+use GraphQL\Type\Definition\InterfaceType;
+use GraphQL\Type\Definition\ObjectType;
+use GraphQL\Type\Definition\ScalarType;
+use GraphQL\Type\Definition\Type;
+use GraphQL\Type\Definition\UnionType;
+use GraphQL\Type\Definition\Directive;
+use GraphQL\Utils;
+
+/**
+ * Class SchemaPrinter
+ * @package GraphQL\Utils
+ */
+class SchemaPrinter
+{
+    public static function doPrint(Schema $schema)
+    {
+        return self::printFilteredSchema($schema, function($n) {
+            return !self::isSpecDirective($n);
+        }, 'self::isDefinedType');
+    }
+
+    public static function printIntrosepctionSchema(Schema $schema)
+    {
+        return self::printFilteredSchema($schema, [__CLASS__, 'isSpecDirective'], [__CLASS__, 'isIntrospectionType']);
+    }
+
+    private static function isSpecDirective($directiveName)
+    {
+        return (
+            $directiveName === 'skip' ||
+            $directiveName === 'include' ||
+            $directiveName === 'deprecated'
+        );
+    }
+
+    private static function isDefinedType($typename)
+    {
+        return !self::isIntrospectionType($typename) && !self::isBuiltInScalar($typename);
+    }
+
+    private static function isIntrospectionType($typename)
+    {
+        return strpos($typename, '__') === 0;
+    }
+
+    private static function isBuiltInScalar($typename)
+    {
+        return (
+            $typename === Type::STRING ||
+            $typename === Type::BOOLEAN ||
+            $typename === Type::INT ||
+            $typename === Type::FLOAT ||
+            $typename === Type::ID
+        );
+    }
+
+    private static function printFilteredSchema(Schema $schema, $directiveFilter, $typeFilter)
+    {
+        $directives = array_filter($schema->getDirectives(), function($directive) use ($directiveFilter) {
+            return $directiveFilter($directive->name);
+        });
+        $typeMap = $schema->getTypeMap();
+        $types = array_filter(array_keys($typeMap), $typeFilter);
+        sort($types);
+        $types = array_map(function($typeName) use ($typeMap) { return $typeMap[$typeName]; }, $types);
+
+        return implode("\n\n", array_filter(array_merge(
+            [self::printSchemaDefinition($schema)],
+            array_map('self::printDirective', $directives),
+            array_map('self::printType', $types)
+        ))) . "\n";
+    }
+
+    private static function printSchemaDefinition(Schema $schema)
+    {
+        if (self::isSchemaOfCommonNames($schema)) {
+            return;
+        }
+
+        $operationTypes = [];
+
+        $queryType = $schema->getQueryType();
+        if ($queryType) {
+            $operationTypes[] = "  query: {$queryType->name}";
+        }
+
+        $mutationType = $schema->getMutationType();
+        if ($mutationType) {
+            $operationTypes[] = "  mutation: {$mutationType->name}";
+        }
+
+        $subscriptionType = $schema->getSubscriptionType();
+        if ($subscriptionType) {
+            $operationTypes[] = "  subscription: {$subscriptionType->name}";
+        }
+
+        return "schema {\n" . implode("\n", $operationTypes) . "\n}";
+    }
+    
+    /**
+     * GraphQL schema define root types for each type of operation. These types are
+     * the same as any other type and can be named in any manner, however there is
+     * a common naming convention:
+     *
+     *   schema {
+     *     query: Query
+     *     mutation: Mutation
+     *   }
+     *
+     * When using this naming convention, the schema description can be omitted.
+     */
+    private static function isSchemaOfCommonNames(Schema $schema)
+    {
+        $queryType = $schema->getQueryType();
+        if ($queryType && $queryType->name !== 'Query') {
+            return false;
+        }
+
+        $mutationType = $schema->getMutationType();
+        if ($mutationType && $mutationType->name !== 'Mutation') {
+            return false;
+        }
+
+        $subscriptionType = $schema->getSubscriptionType();
+        if ($subscriptionType && $subscriptionType->name !== 'Subscription') {
+            return false;
+        }
+
+        return true;
+    }
+
+    public static function printType(Type $type)
+    {
+        if ($type instanceof ScalarType) {
+            return self::printScalar($type);
+        } else if ($type instanceof ObjectType) {
+            return self::printObject($type);
+        } else if ($type instanceof InterfaceType) {
+            return self::printInterface($type);
+        } else if ($type instanceof UnionType) {
+            return self::printUnion($type);
+        } else if ($type instanceof EnumType) {
+            return self::printEnum($type);
+        }
+        Utils::invariant($type instanceof InputObjectType);
+        return self::printInputObject($type);
+    }
+
+    private static function printScalar(ScalarType $type)
+    {
+        return self::printDescription($type) . "scalar {$type->name}";
+    }
+
+    private static function printObject(ObjectType $type)
+    {
+        $interfaces = $type->getInterfaces();
+        $implementedInterfaces = !empty($interfaces) ?
+            ' implements ' . implode(', ', array_map(function($i) {
+                return $i->name;
+            }, $interfaces)) : '';
+        return self::printDescription($type) .
+            "type {$type->name}$implementedInterfaces {\n" .
+                self::printFields($type) . "\n" .
+            "}";
+    }
+
+    private static function printInterface(InterfaceType $type)
+    {
+        return self::printDescription($type) . 
+            "interface {$type->name} {\n" .
+                self::printFields($type) . "\n" .
+            "}";
+    }
+
+    private static function printUnion(UnionType $type)
+    {
+        return self::printDescription($type) .
+            "union {$type->name} = " . implode(" | ", $type->getTypes());
+    }
+
+    private static function printEnum(EnumType $type)
+    {
+        return self::printDescription($type) .
+            "enum {$type->name} {\n" .
+                self::printEnumValues($type->getValues()) . "\n" .
+            "}";
+    }
+
+    private static function printEnumValues($values)
+    {
+        return implode("\n", array_map(function($value, $i) {
+            return self::printDescription($value, '  ', !$i) . '  ' .
+                $value->name . self::printDeprecated($value);
+        }, $values, array_keys($values)));
+    }
+
+    private static function printInputObject(InputObjectType $type)
+    {
+        $fields = array_values($type->getFields());
+        return self::printDescription($type) . 
+            "input {$type->name} {\n" .
+                implode("\n", array_map(function($f, $i) {
+                    return self::printDescription($f, '  ', !$i) . '  ' . self::printInputValue($f);
+                }, $fields, array_keys($fields))) . "\n" .
+            "}";
+    }
+
+    private static function printFields($type)
+    {
+        $fields = array_values($type->getFields());
+        return implode("\n", array_map(function($f, $i) {
+                return self::printDescription($f, '  ', !$i) . '  ' .
+                    $f->name . self::printArgs($f->args, '  ') . ': ' .
+                    (string) $f->getType() . self::printDeprecated($f);
+            }, $fields, array_keys($fields)));
+    }
+
+    private static function printArgs($args, $indentation = '')
+    {
+        if (count($args) === 0) {
+            return '';
+        }
+
+        // If every arg does not have a description, print them on one line.
+        if (Utils::every($args, function($arg) { return empty($arg->description); })) {
+            return '(' . implode(', ', array_map('self::printInputValue', $args)) . ')';
+        }
+
+        return "(\n" . implode("\n", array_map(function($arg, $i) use ($indentation) {
+            return self::printDescription($arg, '  ' . $indentation, !$i) . '  ' . $indentation .
+                self::printInputValue($arg);
+        }, $args, array_keys($args))) . "\n" . $indentation . ')';
+    }
+
+    private static function printInputValue($arg)
+    {
+        $argDecl = $arg->name . ': ' . (string) $arg->getType();
+        if ($arg->defaultValueExists()) {
+            $argDecl .= ' = ' . Printer::doPrint(AST::astFromValue($arg->defaultValue, $arg->getType()));
+        }
+        return $argDecl;
+    }
+
+    private static function printDirective($directive)
+    {
+        return self::printDescription($directive) .
+            'directive @' . $directive->name . self::printArgs($directive->args) .
+            ' on ' . implode(' | ', $directive->locations);
+    }
+
+    private static function printDeprecated($fieldOrEnumVal)
+    {
+        $reason = $fieldOrEnumVal->deprecationReason;
+        if (empty($reason)) {
+            return '';
+        }
+        if ($reason === '' || $reason === Directive::DEFAULT_DEPRECATION_REASON) {
+            return ' @deprecated';
+        }
+        return ' @deprecated(reason: ' .
+            Printer::doPrint(AST::astFromValue($reason, Type::string())) . ')';
+    }
+
+    private static function printDescription($def, $indentation = '', $firstInBlock = true)
+    {
+        if (!$def->description) {
+            return '';
+        }
+        $lines = explode("\n", $def->description);
+        $description = $indentation && !$firstInBlock ? "\n" : '';
+        foreach ($lines as $line) {
+            if ($line === '') {
+                $description .= $indentation . "#\n";
+            } else {
+                // For > 120 character long lines, cut at space boundaries into sublines
+                // of ~80 chars.
+                $sublines = self::breakLine($line, 120 - strlen($indentation));
+                foreach ($sublines as $subline) {
+                    $description .= $indentation . '# ' . $subline . "\n";
+                }
+            }
+        }
+        return $description;
+    }
+
+    private static function breakLine($line, $len)
+    {
+        if (strlen($line) < $len + 5) {
+            return [$line];
+        }
+        preg_match_all("/((?: |^).{15," . ($len - 40) . "}(?= |$))/", $line, $parts);
+        $parts = $parts[0];
+        return array_map(function($part) {
+            return trim($part);
+        }, $parts);
+    }
+}
\ No newline at end of file
diff --git a/tests/Type/IntrospectionTest.php b/tests/Type/IntrospectionTest.php
index ac24e46..8d3f4b9 100644
--- a/tests/Type/IntrospectionTest.php
+++ b/tests/Type/IntrospectionTest.php
@@ -1514,7 +1514,7 @@ class IntrospectionTest extends \PHPUnit_Framework_TestCase
                     'description' => 'A GraphQL Schema defines the capabilities of a ' .
                         'GraphQL server. It exposes all available types and ' .
                         'directives on the server, as well as the entry ' .
-                        'points for query and mutation operations.',
+                        'points for query, mutation, and subscription operations.',
                     'fields' => [
                         [
                             'name' => 'types',
@@ -1571,7 +1571,7 @@ class IntrospectionTest extends \PHPUnit_Framework_TestCase
             'data' => [
                 'typeKindType' => [
                     'name' => '__TypeKind',
-                    'description' => 'An enum describing what kind of type a given __Type is.',
+                    'description' => 'An enum describing what kind of type a given `__Type` is.',
                     'enumValues' => [
                         [
                             'description' => 'Indicates this type is a scalar.',
diff --git a/tests/Utils/BuildSchemaTest.php b/tests/Utils/BuildSchemaTest.php
new file mode 100644
index 0000000..5c2663a
--- /dev/null
+++ b/tests/Utils/BuildSchemaTest.php
@@ -0,0 +1,899 @@
+<?php
+namespace GraphQL\Tests\Utils;
+
+use GraphQL\GraphQL;
+use GraphQL\Language\Parser;
+use GraphQL\Utils\BuildSchema;
+use GraphQL\Utils\SchemaPrinter;
+
+use GraphQL\Type\Definition\Directive;
+use GraphQL\Type\Definition\EnumValueDefinition;
+
+class BuildSchemaTest extends \PHPUnit_Framework_TestCase
+{
+    // Describe: Schema Builder
+
+    private function cycleOutput($body)
+    {
+        $ast = Parser::parse($body);
+        $schema = BuildSchema::buildAST($ast);
+        return "\n" . SchemaPrinter::doPrint($schema);
+    }
+
+    /**
+     * @it can use built schema for limited execution
+     */
+    public function testUseBuiltSchemaForLimitedExecution()
+    {
+        $schema = BuildSchema::buildAST(Parser::parse('
+            schema { query: Query }
+            type Query {
+                str: String
+            }
+        '));
+        
+        $result = GraphQL::execute($schema, '{ str }', ['str' => 123]);
+        $this->assertEquals($result['data'], ['str' => 123]);
+    }
+
+    /**
+     * @it can build a schema directly from the source
+     */
+    public function testBuildSchemaDirectlyFromSource()
+    {
+        $schema = BuildSchema::build("
+            schema { query: Query }
+            type Query {
+                add(x: Int, y: Int): Int
+            }
+        ");
+
+        $result = GraphQL::execute(
+            $schema,
+            '{ add(x: 34, y: 55) }',
+            [
+                'add' => function ($root, $args) {
+                    return $args['x'] + $args['y'];
+                }
+            ]
+        );
+        $this->assertEquals($result, ['data' => ['add' => 89]]);
+    }
+
+    /**
+     * @it Simple Type
+     */
+    public function testSimpleType()
+    {
+        $body = '
+schema {
+  query: HelloScalars
+}
+
+type HelloScalars {
+  str: String
+  int: Int
+  float: Float
+  id: ID
+  bool: Boolean
+}
+';
+        $output = $this->cycleOutput($body);
+        $this->assertEquals($output, $body);
+    }
+
+    /**
+     * @it With directives
+     */
+    public function testWithDirectives()
+    {
+        $body = '
+schema {
+  query: Hello
+}
+
+directive @foo(arg: Int) on FIELD
+
+type Hello {
+  str: String
+}
+';
+        $output = $this->cycleOutput($body);
+        $this->assertEquals($output, $body);
+    }
+
+    /**
+     * @it Supports descriptions
+     */
+    public function testSupportsDescriptions()
+    {
+        $body = '
+schema {
+  query: Hello
+}
+
+# This is a directive
+directive @foo(
+  # It has an argument
+  arg: Int
+) on FIELD
+
+# With an enum
+enum Color {
+  RED
+
+  # Not a creative color
+  GREEN
+  BLUE
+}
+
+# What a great type
+type Hello {
+  # And a field to boot
+  str: String
+}
+';
+        $output = $this->cycleOutput($body);
+        $this->assertEquals($output, $body);
+    }
+
+    /**
+     * @it Maintains @skip & @include
+     */
+    public function testMaintainsSkipAndInclude()
+    {
+        $body = '
+schema {
+  query: Hello
+}
+
+type Hello {
+  str: String
+}
+';
+        $schema = BuildSchema::buildAST(Parser::parse($body));
+        $this->assertEquals(count($schema->getDirectives()), 3);
+        $this->assertEquals($schema->getDirective('skip'), Directive::skipDirective());
+        $this->assertEquals($schema->getDirective('include'), Directive::includeDirective());
+        $this->assertEquals($schema->getDirective('deprecated'), Directive::deprecatedDirective());
+    }
+
+    /**
+     * @it Overriding directives excludes specified
+     */
+    public function testOverridingDirectivesExcludesSpecified()
+    {
+        $body = '
+schema {
+  query: Hello
+}
+
+directive @skip on FIELD
+directive @include on FIELD
+directive @deprecated on FIELD_DEFINITION
+
+type Hello {
+  str: String
+}
+    ';
+        $schema = BuildSchema::buildAST(Parser::parse($body));
+        $this->assertEquals(count($schema->getDirectives()), 3);
+        $this->assertNotEquals($schema->getDirective('skip'), Directive::skipDirective());
+        $this->assertNotEquals($schema->getDirective('include'), Directive::includeDirective());
+        $this->assertNotEquals($schema->getDirective('deprecated'), Directive::deprecatedDirective());
+    }
+
+    /**
+     * @it Type modifiers
+     */
+    public function testTypeModifiers()
+    {
+        $body = '
+schema {
+  query: HelloScalars
+}
+
+type HelloScalars {
+  nonNullStr: String!
+  listOfStrs: [String]
+  listOfNonNullStrs: [String!]
+  nonNullListOfStrs: [String]!
+  nonNullListOfNonNullStrs: [String!]!
+}
+';
+        $output = $this->cycleOutput($body);
+        $this->assertEquals($output, $body);
+    }
+
+    /**
+     * @it Recursive type
+     */
+    public function testRecursiveType()
+    {
+        $body = '
+schema {
+  query: Recurse
+}
+
+type Recurse {
+  str: String
+  recurse: Recurse
+}
+';
+        $output = $this->cycleOutput($body);
+        $this->assertEquals($output, $body);
+    }
+
+    /**
+     * @it Two types circular
+     */
+    public function testTwoTypesCircular()
+    {
+        $body = '
+schema {
+  query: TypeOne
+}
+
+type TypeOne {
+  str: String
+  typeTwo: TypeTwo
+}
+
+type TypeTwo {
+  str: String
+  typeOne: TypeOne
+}
+';
+        $output = $this->cycleOutput($body);
+        $this->assertEquals($output, $body);
+    }
+
+    /**
+     * @it Single argument field
+     */
+    public function testSingleArgumentField()
+    {
+        $body = '
+schema {
+  query: Hello
+}
+
+type Hello {
+  str(int: Int): String
+  floatToStr(float: Float): String
+  idToStr(id: ID): String
+  booleanToStr(bool: Boolean): String
+  strToStr(bool: String): String
+}
+';
+        $output = $this->cycleOutput($body);
+        $this->assertEquals($output, $body);
+    }
+
+    /**
+     * @it Simple type with multiple arguments
+     */
+    public function testSimpleTypeWithMultipleArguments()
+    {
+        $body = '
+schema {
+  query: Hello
+}
+
+type Hello {
+  str(int: Int, bool: Boolean): String
+}
+';
+        $output = $this->cycleOutput($body);
+        $this->assertEquals($output, $body);
+    }
+
+    /**
+     * @it Simple type with interface
+     */
+    public function testSimpleTypeWithInterface()
+    {
+        $body = '
+schema {
+  query: Hello
+}
+
+type Hello implements WorldInterface {
+  str: String
+}
+
+interface WorldInterface {
+  str: String
+}
+';
+        $output = $this->cycleOutput($body);
+        $this->assertEquals($output, $body);
+    }
+
+    /**
+     * @it Simple output enum
+     */
+    public function testSimpleOutputEnum()
+    {
+        $body = '
+schema {
+  query: OutputEnumRoot
+}
+
+enum Hello {
+  WORLD
+}
+
+type OutputEnumRoot {
+  hello: Hello
+}
+';
+        $output = $this->cycleOutput($body);
+        $this->assertEquals($output, $body);
+    }
+
+    /**
+     * @it Multiple value enum
+     */
+    public function testMultipleValueEnum()
+    {
+        $body = '
+schema {
+  query: OutputEnumRoot
+}
+
+enum Hello {
+  WO
+  RLD
+}
+
+type OutputEnumRoot {
+  hello: Hello
+}
+';
+        $output = $this->cycleOutput($body);
+        $this->assertEquals($output, $body);
+    }
+
+    /**
+     * @it Simple Union
+     */
+    public function testSimpleUnion()
+    {
+        $body = '
+schema {
+  query: Root
+}
+
+union Hello = World
+
+type Root {
+  hello: Hello
+}
+
+type World {
+  str: String
+}
+';
+        $output = $this->cycleOutput($body);
+        $this->assertEquals($output, $body);
+    }
+
+    /**
+     * @it Multiple Union
+     */
+    public function testMultipleUnion()
+    {
+        $body = '
+schema {
+  query: Root
+}
+
+union Hello = WorldOne | WorldTwo
+
+type Root {
+  hello: Hello
+}
+
+type WorldOne {
+  str: String
+}
+
+type WorldTwo {
+  str: String
+}
+';
+        $output = $this->cycleOutput($body);
+        $this->assertEquals($output, $body);
+    }
+
+    /**
+     * @it CustomScalar
+     */
+    public function testCustomScalar()
+    {
+        $body = '
+schema {
+  query: Root
+}
+
+scalar CustomScalar
+
+type Root {
+  customScalar: CustomScalar
+}
+';
+        $output = $this->cycleOutput($body);
+        $this->assertEquals($output, $body);
+    }
+
+    /**
+     * @it CustomScalar
+     */
+    public function testInputObject()
+    {
+        $body = '
+schema {
+  query: Root
+}
+
+input Input {
+  int: Int
+}
+
+type Root {
+  field(in: Input): String
+}
+';
+        $output = $this->cycleOutput($body);
+        $this->assertEquals($output, $body);
+    }
+
+    /**
+     * @it Simple argument field with default
+     */
+    public function testSimpleArgumentFieldWithDefault()
+    {
+        $body = '
+schema {
+  query: Hello
+}
+
+type Hello {
+  str(int: Int = 2): String
+}
+';
+        $output = $this->cycleOutput($body);
+        $this->assertEquals($output, $body);
+    }
+
+    /**
+     * @it Simple type with mutation
+     */
+    public function testSimpleTypeWithMutation()
+    {
+        $body = '
+schema {
+  query: HelloScalars
+  mutation: Mutation
+}
+
+type HelloScalars {
+  str: String
+  int: Int
+  bool: Boolean
+}
+
+type Mutation {
+  addHelloScalars(str: String, int: Int, bool: Boolean): HelloScalars
+}
+';
+        $output = $this->cycleOutput($body);
+        $this->assertEquals($output, $body);
+    }
+
+    /**
+     * @it Simple type with subscription
+     */
+    public function testSimpleTypeWithSubscription()
+    {
+        $body = '
+schema {
+  query: HelloScalars
+  subscription: Subscription
+}
+
+type HelloScalars {
+  str: String
+  int: Int
+  bool: Boolean
+}
+
+type Subscription {
+  subscribeHelloScalars(str: String, int: Int, bool: Boolean): HelloScalars
+}
+';
+        $output = $this->cycleOutput($body);
+        $this->assertEquals($output, $body);
+    }
+
+    /**
+     * @it Unreferenced type implementing referenced interface
+     */
+    public function testUnreferencedTypeImplementingReferencedInterface()
+    {
+        $body = '
+type Concrete implements Iface {
+  key: String
+}
+
+interface Iface {
+  key: String
+}
+
+type Query {
+  iface: Iface
+}
+';
+        $output = $this->cycleOutput($body);
+        $this->assertEquals($output, $body);
+    }
+
+    /**
+     * @it Unreferenced type implementing referenced union
+     */
+    public function testUnreferencedTypeImplementingReferencedUnion()
+    {
+        $body = '
+type Concrete {
+  key: String
+}
+
+type Query {
+  union: Union
+}
+
+union Union = Concrete
+';
+        $output = $this->cycleOutput($body);
+        $this->assertEquals($output, $body);
+    }
+
+    /**
+     * @it Supports @deprecated
+     */
+    public function testSupportsDeprecated()
+    {
+        $body = '
+enum MyEnum {
+  VALUE
+  OLD_VALUE @deprecated
+  OTHER_VALUE @deprecated(reason: "Terrible reasons")
+}
+
+type Query {
+  field1: String @deprecated
+  field2: Int @deprecated(reason: "Because I said so")
+  enum: MyEnum
+}
+';
+        $output = $this->cycleOutput($body);
+        $this->assertEquals($output, $body);
+
+        $ast = Parser::parse($body);
+        $schema = BuildSchema::buildAST($ast);
+
+        $this->assertEquals($schema->getType('MyEnum')->getValues(), [
+            new EnumValueDefinition([
+                'name' => 'VALUE',
+                'description' => '',
+                'deprecationReason' => null,
+                'value' => 'VALUE'
+            ]),
+            new EnumValueDefinition([
+                'name' => 'OLD_VALUE',
+                'description' => '',
+                'deprecationReason' => 'No longer supported',
+                'value' => 'OLD_VALUE'
+            ]),
+            new EnumValueDefinition([
+                'name' => 'OTHER_VALUE',
+                'description' => '',
+                'deprecationReason' => 'Terrible reasons',
+                'value' => 'OTHER_VALUE'
+            ])
+        ]);
+
+        $rootFields = $schema->getType('Query')->getFields();
+        $this->assertEquals($rootFields['field1']->isDeprecated(), true);
+        $this->assertEquals($rootFields['field1']->deprecationReason, 'No longer supported');
+
+        $this->assertEquals($rootFields['field2']->isDeprecated(), true);
+        $this->assertEquals($rootFields['field2']->deprecationReason, 'Because I said so');
+    }
+
+    // Describe: Failures
+
+    /**
+     * @it Requires a schema definition or Query type
+     */
+    public function testRequiresSchemaDefinitionOrQueryType()
+    {
+        $this->setExpectedException('GraphQL\Error\Error', 'Must provide schema definition with query type or a type named Query.');
+        $body = '
+type Hello {
+  bar: Bar
+}
+';
+        $doc = Parser::parse($body);
+        BuildSchema::buildAST($doc);
+    }
+
+    /**
+     * @it Allows only a single schema definition
+     */
+    public function testAllowsOnlySingleSchemaDefinition()
+    {
+        $this->setExpectedException('GraphQL\Error\Error', 'Must provide only one schema definition.');
+        $body = '
+schema {
+  query: Hello
+}
+
+schema {
+  query: Hello
+}
+
+type Hello {
+  bar: Bar
+}
+';
+        $doc = Parser::parse($body);
+        BuildSchema::buildAST($doc);
+    }
+
+    /**
+     * @it Requires a query type
+     */
+    public function testRequiresQueryType()
+    {
+        $this->setExpectedException('GraphQL\Error\Error', 'Must provide schema definition with query type or a type named Query.');
+        $body = '
+schema {
+  mutation: Hello
+}
+
+type Hello {
+  bar: Bar
+}
+';
+        $doc = Parser::parse($body);
+        BuildSchema::buildAST($doc);
+    }
+
+    /**
+     * @it Allows only a single query type
+     */
+    public function testAllowsOnlySingleQueryType()
+    {
+        $this->setExpectedException('GraphQL\Error\Error', 'Must provide only one query type in schema.');
+        $body = '
+schema {
+  query: Hello
+  query: Yellow
+}
+
+type Hello {
+  bar: Bar
+}
+
+type Yellow {
+  isColor: Boolean
+}
+';
+        $doc = Parser::parse($body);
+        BuildSchema::buildAST($doc);
+    }
+
+    /**
+     * @it Allows only a single mutation type
+     */
+    public function testAllowsOnlySingleMutationType()
+    {
+        $this->setExpectedException('GraphQL\Error\Error', 'Must provide only one mutation type in schema.');
+        $body = '
+schema {
+  query: Hello
+  mutation: Hello
+  mutation: Yellow
+}
+
+type Hello {
+  bar: Bar
+}
+
+type Yellow {
+  isColor: Boolean
+}
+';
+        $doc = Parser::parse($body);
+        BuildSchema::buildAST($doc);
+    }
+
+    /**
+     * @it Allows only a single subscription type
+     */
+    public function testAllowsOnlySingleSubscriptionType()
+    {
+        $this->setExpectedException('GraphQL\Error\Error', 'Must provide only one subscription type in schema.');
+        $body = '
+schema {
+  query: Hello
+  subscription: Hello
+  subscription: Yellow
+}
+
+type Hello {
+  bar: Bar
+}
+
+type Yellow {
+  isColor: Boolean
+}
+';
+        $doc = Parser::parse($body);
+        BuildSchema::buildAST($doc);
+    }
+
+    /**
+     * @it Unknown type referenced
+     */
+    public function testUnknownTypeReferenced()
+    {
+        $this->setExpectedException('GraphQL\Error\Error', 'Type "Bar" not found in document.');
+        $body = '
+schema {
+  query: Hello
+}
+
+type Hello {
+  bar: Bar
+}
+';
+        $doc = Parser::parse($body);
+        BuildSchema::buildAST($doc);
+    }
+
+    /**
+     * @it Unknown type in interface list
+     */
+    public function testUnknownTypeInInterfaceList()
+    {
+        $this->setExpectedException('GraphQL\Error\Error', 'Type "Bar" not found in document.');
+        $body = '
+schema {
+  query: Hello
+}
+
+type Hello implements Bar { }
+';
+        $doc = Parser::parse($body);
+        BuildSchema::buildAST($doc);
+    }
+
+    /**
+     * @it Unknown type in union list
+     */
+    public function testUnknownTypeInUnionList()
+    {
+        $this->setExpectedException('GraphQL\Error\Error', 'Type "Bar" not found in document.');
+        $body = '
+schema {
+  query: Hello
+}
+
+union TestUnion = Bar
+type Hello { testUnion: TestUnion }
+';
+        $doc = Parser::parse($body);
+        BuildSchema::buildAST($doc);
+    }
+
+    /**
+     * @it Unknown query type
+     */
+    public function testUnknownQueryType()
+    {
+        $this->setExpectedException('GraphQL\Error\Error', 'Specified query type "Wat" not found in document.');
+        $body = '
+schema {
+  query: Wat
+}
+
+type Hello {
+  str: String
+}
+';
+        $doc = Parser::parse($body);
+        BuildSchema::buildAST($doc);
+    }
+
+    /**
+     * @it Unknown mutation type
+     */
+    public function testUnknownMutationType()
+    {
+        $this->setExpectedException('GraphQL\Error\Error', 'Specified mutation type "Wat" not found in document.');
+        $body = '
+schema {
+  query: Hello
+  mutation: Wat
+}
+
+type Hello {
+  str: String
+}
+';
+        $doc = Parser::parse($body);
+        BuildSchema::buildAST($doc);
+    }
+
+    /**
+     * @it Unknown subscription type
+     */
+    public function testUnknownSubscriptionType()
+    {
+        $this->setExpectedException('GraphQL\Error\Error', 'Specified subscription type "Awesome" not found in document.');
+        $body = '
+schema {
+  query: Hello
+  mutation: Wat
+  subscription: Awesome
+}
+
+type Hello {
+  str: String
+}
+
+type Wat {
+  str: String
+}
+';
+        $doc = Parser::parse($body);
+        BuildSchema::buildAST($doc);
+    }
+
+    /**
+     * @it Does not consider operation names
+     */
+    public function testDoesNotConsiderOperationNames()
+    {
+        $this->setExpectedException('GraphQL\Error\Error', 'Specified query type "Foo" not found in document.');
+        $body = '
+schema {
+  query: Foo
+}
+
+query Foo { field }
+';
+        $doc = Parser::parse($body);
+        BuildSchema::buildAST($doc);
+    }
+
+    /**
+     * @it Does not consider fragment names
+     */
+    public function testDoesNotConsiderFragmentNames()
+    {
+        $this->setExpectedException('GraphQL\Error\Error', 'Specified query type "Foo" not found in document.');
+        $body = '
+schema {
+  query: Foo
+}
+
+fragment Foo on Type { field }
+';
+        $doc = Parser::parse($body);
+        BuildSchema::buildAST($doc);
+    }
+}
diff --git a/tests/Utils/SchemaPrinterTest.php b/tests/Utils/SchemaPrinterTest.php
new file mode 100644
index 0000000..49314f0
--- /dev/null
+++ b/tests/Utils/SchemaPrinterTest.php
@@ -0,0 +1,850 @@
+<?php
+namespace GraphQL\Tests\Utils;
+
+use GraphQL\GraphQL;
+use GraphQL\Schema;
+use GraphQL\Type\Definition\CustomScalarType;
+use GraphQL\Type\Definition\InputObjectType;
+use GraphQL\Type\Definition\InterfaceType;
+use GraphQL\Type\Definition\ObjectType;
+use GraphQL\Type\Definition\Type;
+use GraphQL\Type\Definition\EnumType;
+use GraphQL\Type\Definition\UnionType;
+use GraphQL\Utils\SchemaPrinter;
+
+class SchemaPrinterTest extends \PHPUnit_Framework_TestCase
+{
+    // Describe: Type System Printer
+
+    private function printForTest($schema)
+    {
+        return "\n" . SchemaPrinter::doPrint($schema);
+    }
+
+    private function printSingleFieldSchema($fieldConfig)
+    {
+        $root = new ObjectType([
+            'name' => 'Root',
+            'fields' => [
+                'singleField' => $fieldConfig
+            ]
+        ]);
+        return $this->printForTest(new Schema(['query' => $root]));
+    }
+
+    /**
+     * @it Prints String Field
+     */
+    public function testPrintsStringField()
+    {
+        $output = $this->printSingleFieldSchema([
+            'type' => Type::string()
+        ]);
+        $this->assertEquals($output, '
+schema {
+  query: Root
+}
+
+type Root {
+  singleField: String
+}
+');
+    }
+
+    /**
+     * @it Prints [String] Field
+     */
+    public function testPrintArrayStringField()
+    {
+        $output = $this->printSingleFieldSchema([
+            'type' => Type::listOf(Type::string())
+        ]);
+        $this->assertEquals($output, '
+schema {
+  query: Root
+}
+
+type Root {
+  singleField: [String]
+}
+');
+    }
+
+    /**
+     * @it Prints String! Field
+     */
+    public function testPrintNonNullStringField()
+    {
+        $output = $this->printSingleFieldSchema([
+            'type' => Type::nonNull(Type::string())
+        ]);
+        $this->assertEquals($output, '
+schema {
+  query: Root
+}
+
+type Root {
+  singleField: String!
+}
+');
+    }
+
+    /**
+     * @it Prints [String]! Field
+     */
+    public function testPrintNonNullArrayStringField()
+    {
+        $output = $this->printSingleFieldSchema([
+            'type' => Type::nonNull(Type::listOf(Type::string()))
+        ]);
+        $this->assertEquals($output, '
+schema {
+  query: Root
+}
+
+type Root {
+  singleField: [String]!
+}
+');
+    }
+
+    /**
+     * @it Prints [String!] Field
+     */
+    public function testPrintArrayNonNullStringField()
+    {
+        $output = $this->printSingleFieldSchema([
+            'type' => Type::listOf(Type::nonNull(Type::string()))
+        ]);
+        $this->assertEquals($output, '
+schema {
+  query: Root
+}
+
+type Root {
+  singleField: [String!]
+}
+');
+    }
+
+    /**
+     * @it Prints [String!]! Field
+     */
+    public function testPrintNonNullArrayNonNullStringField()
+    {
+        $output = $this->printSingleFieldSchema([
+            'type' => Type::nonNull(Type::listOf(Type::nonNull(Type::string())))
+        ]);
+        $this->assertEquals($output, '
+schema {
+  query: Root
+}
+
+type Root {
+  singleField: [String!]!
+}
+');
+    }
+
+    /**
+     * @it Prints Object Field
+     */
+    public function testPrintObjectField()
+    {
+        $fooType = new ObjectType([
+            'name' => 'Foo',
+            'fields' => ['str' => ['type' => Type::string()]]
+        ]);
+
+        $root = new ObjectType([
+            'name' => 'Root',
+            'fields' => ['foo' => ['type' => $fooType]]
+        ]);
+
+        $schema = new Schema(['query' => $root]);
+        $output = $this->printForTest($schema);
+        $this->assertEquals($output, '
+schema {
+  query: Root
+}
+
+type Foo {
+  str: String
+}
+
+type Root {
+  foo: Foo
+}
+');
+    }
+
+    /**
+     * @it Prints String Field With Int Arg
+     */
+    public function testPrintsStringFieldWithIntArg()
+    {
+        $output = $this->printSingleFieldSchema([
+            'type' => Type::string(),
+            'args' => ['argOne' => ['type' => Type::int()]]
+        ]);
+        $this->assertEquals($output, '
+schema {
+  query: Root
+}
+
+type Root {
+  singleField(argOne: Int): String
+}
+');
+    }
+
+    /**
+     * @it Prints String Field With Int Arg With Default
+     */
+    public function testPrintsStringFieldWithIntArgWithDefault()
+    {
+        $output = $this->printSingleFieldSchema([
+            'type' => Type::string(),
+            'args' => ['argOne' => ['type' => Type::int(), 'defaultValue' => 2]]
+        ]);
+        $this->assertEquals($output, '
+schema {
+  query: Root
+}
+
+type Root {
+  singleField(argOne: Int = 2): String
+}
+');
+    }
+
+    /**
+     * @it Prints String Field With Int Arg With Default Null
+     */
+    public function testPrintsStringFieldWithIntArgWithDefaultNull()
+    {
+        $output = $this->printSingleFieldSchema([
+            'type' => Type::string(),
+            'args' => ['argOne' => ['type' => Type::int(), 'defaultValue' => null]]
+        ]);
+        $this->assertEquals($output, '
+schema {
+  query: Root
+}
+
+type Root {
+  singleField(argOne: Int = null): String
+}
+');
+    }
+
+    /**
+     * @it Prints String Field With Int! Arg
+     */
+    public function testPrintsStringFieldWithNonNullIntArg()
+    {
+        $output = $this->printSingleFieldSchema([
+            'type' => Type::string(),
+            'args' => ['argOne' => ['type' => Type::nonNull(Type::int())]]
+        ]);
+        $this->assertEquals($output, '
+schema {
+  query: Root
+}
+
+type Root {
+  singleField(argOne: Int!): String
+}
+');
+    }
+
+    /**
+     * @it Prints String Field With Multiple Args
+     */
+    public function testPrintsStringFieldWithMultipleArgs()
+    {
+        $output = $this->printSingleFieldSchema([
+            'type' => Type::string(),
+            'args' => [
+                'argOne' => ['type' => Type::int()],
+                'argTwo' => ['type' => Type::string()]
+            ]
+        ]);
+        $this->assertEquals($output, '
+schema {
+  query: Root
+}
+
+type Root {
+  singleField(argOne: Int, argTwo: String): String
+}
+');
+    }
+
+    /**
+     * @it Prints String Field With Multiple Args, First is Default
+     */
+    public function testPrintsStringFieldWithMultipleArgsFirstIsDefault()
+    {
+        $output = $this->printSingleFieldSchema([
+            'type' => Type::string(),
+            'args' => [
+                'argOne' => ['type' => Type::int(), 'defaultValue' => 1],
+                'argTwo' => ['type' => Type::string()],
+                'argThree' => ['type' => Type::boolean()]
+            ]
+        ]);
+        $this->assertEquals($output, '
+schema {
+  query: Root
+}
+
+type Root {
+  singleField(argOne: Int = 1, argTwo: String, argThree: Boolean): String
+}
+');
+    }
+
+    /**
+     * @it Prints String Field With Multiple Args, Second is Default
+     */
+    public function testPrintsStringFieldWithMultipleArgsSecondIsDefault()
+    {
+        $output = $this->printSingleFieldSchema([
+            'type' => Type::string(),
+            'args' => [
+                'argOne' => ['type' => Type::int()],
+                'argTwo' => ['type' => Type::string(), 'defaultValue' => 'foo'],
+                'argThree' => ['type' => Type::boolean()]
+            ]
+        ]);
+        $this->assertEquals($output, '
+schema {
+  query: Root
+}
+
+type Root {
+  singleField(argOne: Int, argTwo: String = "foo", argThree: Boolean): String
+}
+');
+    }
+
+    /**
+     * @it Prints String Field With Multiple Args, Last is Default
+     */
+    public function testPrintsStringFieldWithMultipleArgsLastIsDefault()
+    {
+        $output = $this->printSingleFieldSchema([
+            'type' => Type::string(),
+            'args' => [
+                'argOne' => ['type' => Type::int()],
+                'argTwo' => ['type' => Type::string()],
+                'argThree' => ['type' => Type::boolean(), 'defaultValue' => false]
+            ]
+        ]);
+        $this->assertEquals($output, '
+schema {
+  query: Root
+}
+
+type Root {
+  singleField(argOne: Int, argTwo: String, argThree: Boolean = false): String
+}
+');
+    }
+
+    /**
+     * @it Print Interface
+     */
+    public function testPrintInterface()
+    {
+        $fooType = new InterfaceType([
+            'name' => 'Foo',
+            'resolveType' => function() { return null; },
+            'fields' => ['str' => ['type' => Type::string()]]
+        ]);
+
+        $barType = new ObjectType([
+            'name' => 'Bar',
+            'fields' => ['str' => ['type' => Type::string()]],
+            'interfaces' => [$fooType]
+        ]);
+
+        $root = new ObjectType([
+            'name' => 'Root',
+            'fields' => ['bar' => ['type' => $barType]]
+        ]);
+
+        $schema = new Schema([
+            'query' => $root,
+            'types' => [$barType]
+        ]);
+        $output = $this->printForTest($schema);
+        $this->assertEquals($output, '
+schema {
+  query: Root
+}
+
+type Bar implements Foo {
+  str: String
+}
+
+interface Foo {
+  str: String
+}
+
+type Root {
+  bar: Bar
+}
+');
+    }
+
+    /**
+     * @it Print Multiple Interface
+     */
+    public function testPrintMultipleInterface()
+    {
+        $fooType = new InterfaceType([
+            'name' => 'Foo',
+            'resolveType' => function() { return null; },
+            'fields' => ['str' => ['type' => Type::string()]]
+        ]);
+
+        $baazType = new InterfaceType([
+            'name' => 'Baaz',
+            'resolveType' => function() { return null; },
+            'fields' => ['int' => ['type' => Type::int()]]
+        ]);
+
+        $barType = new ObjectType([
+            'name' => 'Bar',
+            'fields' => [
+                'str' => ['type' => Type::string()],
+                'int' => ['type' => Type::int()]
+            ],
+            'interfaces' => [$fooType, $baazType]
+        ]);
+
+        $root = new ObjectType([
+            'name' => 'Root',
+            'fields' => ['bar' => ['type' => $barType]]
+        ]);
+
+        $schema = new Schema([
+            'query' => $root,
+            'types' => [$barType]
+        ]);
+        $output = $this->printForTest($schema);
+        $this->assertEquals($output, '
+schema {
+  query: Root
+}
+
+interface Baaz {
+  int: Int
+}
+
+type Bar implements Foo, Baaz {
+  str: String
+  int: Int
+}
+
+interface Foo {
+  str: String
+}
+
+type Root {
+  bar: Bar
+}
+');
+    }
+
+    /**
+     * @it Print Unions
+     */
+    public function testPrintUnions()
+    {
+        $fooType = new ObjectType([
+            'name' => 'Foo',
+            'fields' => ['bool' => ['type' => Type::boolean()]]
+        ]);
+
+        $barType = new ObjectType([
+            'name' => 'Bar',
+            'fields' => ['str' => ['type' => Type::string()]]
+        ]);
+
+        $singleUnion = new UnionType([
+            'name' => 'SingleUnion',
+            'resolveType' => function() { return null; },
+            'types' => [$fooType]
+        ]);
+
+        $multipleUnion = new UnionType([
+            'name' => 'MultipleUnion',
+            'resolveType' => function() { return null; },
+            'types' => [$fooType, $barType]
+        ]);
+
+        $root = new ObjectType([
+            'name' => 'Root',
+            'fields' => [
+                'single' => ['type' => $singleUnion],
+                'multiple' => ['type' => $multipleUnion]
+            ]
+        ]);
+
+        $schema = new Schema(['query' => $root]);
+        $output = $this->printForTest($schema);
+        $this->assertEquals($output, '
+schema {
+  query: Root
+}
+
+type Bar {
+  str: String
+}
+
+type Foo {
+  bool: Boolean
+}
+
+union MultipleUnion = Foo | Bar
+
+type Root {
+  single: SingleUnion
+  multiple: MultipleUnion
+}
+
+union SingleUnion = Foo
+');
+    }
+
+    /**
+     * @it Print Input Type
+     */
+    public function testInputType()
+    {
+        $inputType = new InputObjectType([
+            'name' => 'InputType',
+            'fields' => ['int' => ['type' => Type::int()]]
+        ]);
+
+        $root = new ObjectType([
+            'name' => 'Root',
+            'fields' => [
+                'str' => [
+                    'type' => Type::string(),
+                    'args' => ['argOne' => ['type' => $inputType]]
+                ]
+            ]
+        ]);
+
+        $schema = new Schema(['query' => $root]);
+        $output = $this->printForTest($schema);
+        $this->assertEquals($output, '
+schema {
+  query: Root
+}
+
+input InputType {
+  int: Int
+}
+
+type Root {
+  str(argOne: InputType): String
+}
+');
+    }
+
+    /**
+     * @it Custom Scalar
+     */
+    public function testCustomScalar()
+    {
+        $oddType = new CustomScalarType([
+            'name' => 'Odd',
+            'serialize' => function($value) {
+                return $value % 2 === 1 ? $value : null;
+            }
+        ]);
+
+        $root = new ObjectType([
+            'name' => 'Root',
+            'fields' => [
+                'odd' => ['type' => $oddType]
+            ]
+        ]);
+
+        $schema = new Schema(['query' => $root]);
+        $output = $this->printForTest($schema);
+        $this->assertEquals($output, '
+schema {
+  query: Root
+}
+
+scalar Odd
+
+type Root {
+  odd: Odd
+}
+');
+    }
+
+    /**
+     * @it Enum
+     */
+    public function testEnum()
+    {
+        $RGBType = new EnumType([
+            'name' => 'RGB',
+            'values' => [
+                'RED' => ['value' => 0],
+                'GREEN' => ['value' => 1],
+                'BLUE' => ['value' => 2]
+            ]
+        ]);
+
+        $root = new ObjectType([
+            'name' => 'Root',
+            'fields' => [
+                'rgb' => ['type' => $RGBType]
+            ]
+        ]);
+
+        $schema = new Schema(['query' => $root]);
+        $output = $this->printForTest($schema);
+        $this->assertEquals($output, '
+schema {
+  query: Root
+}
+
+enum RGB {
+  RED
+  GREEN
+  BLUE
+}
+
+type Root {
+  rgb: RGB
+}
+');
+    }
+
+    /**
+     * @it Print Introspection Schema
+     */
+    public function testPrintIntrospectionSchema()
+    {
+        $root = new ObjectType([
+            'name' => 'Root',
+            'fields' => [
+                'onlyField' => ['type' => Type::string()]
+            ]
+        ]);
+
+        $schema = new Schema(['query' => $root]);
+        $output = SchemaPrinter::printIntrosepctionSchema($schema);
+        $introspectionSchema = <<<'EOT'
+schema {
+  query: Root
+}
+
+# Directs the executor to include this field or fragment only when the `if` argument is true.
+directive @include(
+  # Included when true.
+  if: Boolean!
+) on FIELD | FRAGMENT_SPREAD | INLINE_FRAGMENT
+
+# Directs the executor to skip this field or fragment when the `if` argument is true.
+directive @skip(
+  # Skipped when true.
+  if: Boolean!
+) on FIELD | FRAGMENT_SPREAD | INLINE_FRAGMENT
+
+# Marks an element of a GraphQL schema as no longer supported.
+directive @deprecated(
+  # Explains why this element was deprecated, usually also including a suggestion
+  # for how to access supported similar data. Formatted in
+  # [Markdown](https://daringfireball.net/projects/markdown/).
+  reason: String = "No longer supported"
+) on FIELD_DEFINITION | ENUM_VALUE
+
+# A Directive provides a way to describe alternate runtime execution and type validation behavior in a GraphQL document.
+#
+# In some cases, you need to provide options to alter GraphQL's execution behavior
+# in ways field arguments will not suffice, such as conditionally including or
+# skipping a field. Directives provide this by describing additional information
+# to the executor.
+type __Directive {
+  name: String!
+  description: String
+  locations: [__DirectiveLocation!]!
+  args: [__InputValue!]!
+  onOperation: Boolean! @deprecated(reason: "Use `locations`.")
+  onFragment: Boolean! @deprecated(reason: "Use `locations`.")
+  onField: Boolean! @deprecated(reason: "Use `locations`.")
+}
+
+# A Directive can be adjacent to many parts of the GraphQL language, a
+# __DirectiveLocation describes one such possible adjacencies.
+enum __DirectiveLocation {
+  # Location adjacent to a query operation.
+  QUERY
+
+  # Location adjacent to a mutation operation.
+  MUTATION
+
+  # Location adjacent to a subscription operation.
+  SUBSCRIPTION
+
+  # Location adjacent to a field.
+  FIELD
+
+  # Location adjacent to a fragment definition.
+  FRAGMENT_DEFINITION
+
+  # Location adjacent to a fragment spread.
+  FRAGMENT_SPREAD
+
+  # Location adjacent to an inline fragment.
+  INLINE_FRAGMENT
+
+  # Location adjacent to a schema definition.
+  SCHEMA
+
+  # Location adjacent to a scalar definition.
+  SCALAR
+
+  # Location adjacent to an object type definition.
+  OBJECT
+
+  # Location adjacent to a field definition.
+  FIELD_DEFINITION
+
+  # Location adjacent to an argument definition.
+  ARGUMENT_DEFINITION
+
+  # Location adjacent to an interface definition.
+  INTERFACE
+
+  # Location adjacent to a union definition.
+  UNION
+
+  # Location adjacent to an enum definition.
+  ENUM
+
+  # Location adjacent to an enum value definition.
+  ENUM_VALUE
+
+  # Location adjacent to an input object type definition.
+  INPUT_OBJECT
+
+  # Location adjacent to an input object field definition.
+  INPUT_FIELD_DEFINITION
+}
+
+# One possible value for a given Enum. Enum values are unique values, not a
+# placeholder for a string or numeric value. However an Enum value is returned in
+# a JSON response as a string.
+type __EnumValue {
+  name: String!
+  description: String
+  isDeprecated: Boolean!
+  deprecationReason: String
+}
+
+# Object and Interface types are described by a list of Fields, each of which has
+# a name, potentially a list of arguments, and a return type.
+type __Field {
+  name: String!
+  description: String
+  args: [__InputValue!]!
+  type: __Type!
+  isDeprecated: Boolean!
+  deprecationReason: String
+}
+
+# Arguments provided to Fields or Directives and the input fields of an
+# InputObject are represented as Input Values which describe their type and
+# optionally a default value.
+type __InputValue {
+  name: String!
+  description: String
+  type: __Type!
+
+  # A GraphQL-formatted string representing the default value for this input value.
+  defaultValue: String
+}
+
+# A GraphQL Schema defines the capabilities of a GraphQL server. It exposes all
+# available types and directives on the server, as well as the entry points for
+# query, mutation, and subscription operations.
+type __Schema {
+  # A list of all types supported by this server.
+  types: [__Type!]!
+
+  # The type that query operations will be rooted at.
+  queryType: __Type!
+
+  # If this server supports mutation, the type that mutation operations will be rooted at.
+  mutationType: __Type
+
+  # If this server support subscription, the type that subscription operations will be rooted at.
+  subscriptionType: __Type
+
+  # A list of all directives supported by this server.
+  directives: [__Directive!]!
+}
+
+# The fundamental unit of any GraphQL Schema is the type. There are many kinds of
+# types in GraphQL as represented by the `__TypeKind` enum.
+#
+# Depending on the kind of a type, certain fields describe information about that
+# type. Scalar types provide no information beyond a name and description, while
+# Enum types provide their values. Object and Interface types provide the fields
+# they describe. Abstract types, Union and Interface, provide the Object types
+# possible at runtime. List and NonNull types compose other types.
+type __Type {
+  kind: __TypeKind!
+  name: String
+  description: String
+  fields(includeDeprecated: Boolean = false): [__Field!]
+  interfaces: [__Type!]
+  possibleTypes: [__Type!]
+  enumValues(includeDeprecated: Boolean = false): [__EnumValue!]
+  inputFields: [__InputValue!]
+  ofType: __Type
+}
+
+# An enum describing what kind of type a given `__Type` is.
+enum __TypeKind {
+  # Indicates this type is a scalar.
+  SCALAR
+
+  # Indicates this type is an object. `fields` and `interfaces` are valid fields.
+  OBJECT
+
+  # Indicates this type is an interface. `fields` and `possibleTypes` are valid fields.
+  INTERFACE
+
+  # Indicates this type is a union. `possibleTypes` is a valid field.
+  UNION
+
+  # Indicates this type is an enum. `enumValues` is a valid field.
+  ENUM
+
+  # Indicates this type is an input object. `inputFields` is a valid field.
+  INPUT_OBJECT
+
+  # Indicates this type is a list. `ofType` is a valid field.
+  LIST
+
+  # Indicates this type is a non-null. `ofType` is a valid field.
+  NON_NULL
+}
+
+EOT;
+        $this->assertEquals($output, $introspectionSchema);
+    }
+}
\ No newline at end of file