diff --git a/src/Executor/Executor.php b/src/Executor/Executor.php
index 998038d..b2ba19a 100644
--- a/src/Executor/Executor.php
+++ b/src/Executor/Executor.php
@@ -1053,15 +1053,6 @@ class Executor
         $runtimeType = $returnType->resolveType($result, $exeContext->contextValue, $info);
 
         if (null === $runtimeType) {
-            if ($returnType instanceof InterfaceType && $info->schema->getConfig()->typeLoader) {
-                Warning::warnOnce(
-                    "GraphQL Interface Type `{$returnType->name}` returned `null` from it`s `resolveType` function ".
-                    'for value: ' . Utils::printSafe($result) . '. Switching to slow resolution method using `isTypeOf` ' .
-                    'of all possible implementations. It requires full schema scan and degrades query performance significantly. '.
-                    ' Make sure your `resolveType` always returns valid implementation or throws.',
-                    Warning::WARNING_FULL_SCHEMA_SCAN
-                );
-            }
             $runtimeType = self::defaultTypeResolver($result, $exeContext->contextValue, $info, $returnType);
         }
 
@@ -1122,9 +1113,11 @@ class Executor
 
         if (!$runtimeType instanceof ObjectType) {
             throw new InvariantViolation(
-                "Abstract type {$returnType} must resolve to an Object type at runtime " .
-                "for field {$info->parentType}.{$info->fieldName} with " .
-                'value "' . Utils::printSafe($result) . '", received "'. Utils::printSafe($runtimeType) . '".'
+                "Abstract type {$returnType} must resolve to an Object type at " .
+                "runtime for field {$info->parentType}.{$info->fieldName} with " .
+                'value "' . Utils::printSafe($result) . '", received "'. Utils::printSafe($runtimeType) . '".' .
+                'Either the ' . $returnType . ' type should provide a "resolveType" ' .
+                'function or each possible types should provide an "isTypeOf" function.'
             );
         }
 
@@ -1307,7 +1300,12 @@ class Executor
 
     /**
      * If a resolveType function is not given, then a default resolve behavior is
-     * used which tests each possible type for the abstract type by calling
+     * used which attempts two strategies:
+     *
+     * First, See if the provided value has a `__typename` field defined, if so, use
+     * that value as name of the resolved type.
+     *
+     * Otherwise, test each possible type for the abstract type by calling
      * isTypeOf for the object being coerced, returning the first type that matches.
      *
      * @param $value
@@ -1318,6 +1316,27 @@ class Executor
      */
     private function defaultTypeResolver($value, $context, ResolveInfo $info, AbstractType $abstractType)
     {
+        // First, look for `__typename`.
+        if (
+            $value !== null &&
+            is_array($value) &&
+            isset($value['__typename']) &&
+            is_string($value['__typename'])
+        ) {
+            return $value['__typename'];
+        }
+
+        if ($abstractType instanceof InterfaceType && $info->schema->getConfig()->typeLoader) {
+            Warning::warnOnce(
+                "GraphQL Interface Type `{$abstractType->name}` returned `null` from it`s `resolveType` function ".
+                'for value: ' . Utils::printSafe($value) . '. Switching to slow resolution method using `isTypeOf` ' .
+                'of all possible implementations. It requires full schema scan and degrades query performance significantly. '.
+                ' Make sure your `resolveType` always returns valid implementation or throws.',
+                Warning::WARNING_FULL_SCHEMA_SCAN
+            );
+        }
+
+        // Otherwise, test each possible type.
         $possibleTypes = $info->schema->getPossibleTypes($abstractType);
         $promisedIsTypeOfResults = [];
 
diff --git a/src/Type/Definition/ObjectType.php b/src/Type/Definition/ObjectType.php
index 43d2355..d77a731 100644
--- a/src/Type/Definition/ObjectType.php
+++ b/src/Type/Definition/ObjectType.php
@@ -240,15 +240,6 @@ class ObjectType extends Type implements OutputType, CompositeType
                 "{$this->name} may declare it implements {$iface->name} only once."
             );
             $implemented[$iface->name] = true;
-            if (!isset($iface->config['resolveType'])) {
-                Utils::invariant(
-                    isset($this->config['isTypeOf']),
-                    "Interface Type {$iface->name} does not provide a \"resolveType\" " .
-                    "function and implementing Type {$this->name} does not provide a " .
-                    '"isTypeOf" function. There is no way to resolve this implementing ' .
-                    'type during execution.'
-                );
-            }
         }
     }
 }
diff --git a/src/Type/Definition/UnionType.php b/src/Type/Definition/UnionType.php
index 49855b7..06d57fc 100644
--- a/src/Type/Definition/UnionType.php
+++ b/src/Type/Definition/UnionType.php
@@ -158,15 +158,6 @@ class UnionType extends Type implements AbstractType, OutputType, CompositeType
                 "{$this->name} can include {$objType->name} type only once."
             );
             $includedTypeNames[$objType->name] = true;
-            if (!isset($this->config['resolveType'])) {
-                Utils::invariant(
-                    isset($objType->config['isTypeOf']) && is_callable($objType->config['isTypeOf']),
-                    "Union type \"{$this->name}\" does not provide a \"resolveType\" " .
-                    "function and possible type \"{$objType->name}\" does not provide an " .
-                    '"isTypeOf" function. There is no way to resolve this possible type ' .
-                    'during execution.'
-                );
-            }
         }
     }
 }
diff --git a/src/Utils/BuildSchema.php b/src/Utils/BuildSchema.php
index 078427a..9dc966c 100644
--- a/src/Utils/BuildSchema.php
+++ b/src/Utils/BuildSchema.php
@@ -216,21 +216,21 @@ class BuildSchema
         $directives = array_map([$this, 'getDirective'], $directiveDefs);
 
         // If specified directives were not explicitly declared, add them.
-        $skip = array_reduce($directives, function($hasSkip, $directive) {
+        $skip = array_reduce($directives, function ($hasSkip, $directive) {
             return $hasSkip || $directive->name == 'skip';
         });
         if (!$skip) {
             $directives[] = Directive::skipDirective();
         }
 
-        $include = array_reduce($directives, function($hasInclude, $directive) {
+        $include = array_reduce($directives, function ($hasInclude, $directive) {
             return $hasInclude || $directive->name == 'include';
         });
         if (!$include) {
             $directives[] = Directive::includeDirective();
         }
 
-        $deprecated = array_reduce($directives, function($hasDeprecated, $directive) {
+        $deprecated = array_reduce($directives, function ($hasDeprecated, $directive) {
             return $hasDeprecated || $directive->name == 'deprecated';
         });
         if (!$deprecated) {
@@ -245,12 +245,12 @@ class BuildSchema
             'subscription' => $subscriptionTypeName ?
                 $this->getObjectType($this->nodeMap[$subscriptionTypeName]) :
                 null,
-            'typeLoader' => function($name) {
+            'typeLoader' => function ($name) {
                 return $this->typeDefNamed($name);
             },
             'directives' => $directives,
             'astNode' => $schemaDef,
-            'types' => function() {
+            'types' => function () {
                 $types = [];
                 foreach ($this->nodeMap as $name => $def) {
                     if (!isset($this->loadedTypeDefs[$name])) {
@@ -269,7 +269,7 @@ class BuildSchema
         return new Directive([
             'name' => $directiveNode->name->value,
             'description' => $this->getDescription($directiveNode),
-            'locations' => Utils::map($directiveNode->locations, function($node) {
+            'locations' => Utils::map($directiveNode->locations, function ($node) {
                 return $node->value;
             }),
             'args' => $directiveNode->arguments ? FieldArgument::createMap($this->makeInputValues($directiveNode->arguments)) : null,
@@ -342,7 +342,7 @@ class BuildSchema
                 $config = $fn($config, $this->nodeMap[$typeName], $this->nodeMap);
             } catch (\Exception $e) {
                 throw new Error(
-                    "Type config decorator passed to " . (static::class) . " threw an error ".
+                    "Type config decorator passed to " . (static::class) . " threw an error " .
                     "when building $typeName type: {$e->getMessage()}",
                     null,
                     null,
@@ -352,7 +352,7 @@ class BuildSchema
                 );
             } catch (\Throwable $e) {
                 throw new Error(
-                    "Type config decorator passed to " . (static::class) . " threw an error ".
+                    "Type config decorator passed to " . (static::class) . " threw an error " .
                     "when building $typeName type: {$e->getMessage()}",
                     null,
                     null,
@@ -363,7 +363,7 @@ class BuildSchema
             }
             if (!is_array($config) || isset($config[0])) {
                 throw new Error(
-                    "Type config decorator passed to " . (static::class) . " is expected to return an array, but got ".
+                    "Type config decorator passed to " . (static::class) . " is expected to return an array, but got " .
                     Utils::getVariableType($config)
                 );
             }
@@ -433,10 +433,10 @@ class BuildSchema
         return [
             'name' => $typeName,
             'description' => $this->getDescription($def),
-            'fields' => function() use ($def) {
+            'fields' => function () use ($def) {
                 return $this->makeFieldDefMap($def);
             },
-            'interfaces' => function() use ($def) {
+            'interfaces' => function () use ($def) {
                 return $this->makeImplementedInterfaces($def);
             },
             'astNode' => $def
@@ -450,7 +450,7 @@ class BuildSchema
             function ($field) {
                 return $field->name->value;
             },
-            function($field) {
+            function ($field) {
                 return [
                     'type' => $this->produceOutputType($field->type),
                     'description' => $this->getDescription($field),
@@ -479,7 +479,7 @@ class BuildSchema
             function ($value) {
                 return $value->name->value;
             },
-            function($value) {
+            function ($value) {
                 $type = $this->produceInputType($value->type);
                 $config = [
                     'name' => $value->name->value,
@@ -501,13 +501,10 @@ class BuildSchema
         return [
             'name' => $typeName,
             'description' => $this->getDescription($def),
-            'fields' => function() use ($def) {
+            'fields' => function () use ($def) {
                 return $this->makeFieldDefMap($def);
             },
-            'astNode' => $def,
-            'resolveType' => function() {
-                $this->cannotExecuteSchema();
-            }
+            'astNode' => $def
         ];
     }
 
@@ -519,10 +516,10 @@ class BuildSchema
             'astNode' => $def,
             'values' => Utils::keyValMap(
                 $def->values,
-                function($enumValue) {
+                function ($enumValue) {
                     return $enumValue->name->value;
                 },
-                function($enumValue) {
+                function ($enumValue) {
                     return [
                         'description' => $this->getDescription($enumValue),
                         'deprecationReason' => $this->getDeprecationReason($enumValue),
@@ -538,11 +535,10 @@ class BuildSchema
         return [
             'name' => $def->name->value,
             'description' => $this->getDescription($def),
-            'types' => Utils::map($def->types, function($typeNode) {
+            'types' => Utils::map($def->types, function ($typeNode) {
                 return $this->produceObjectType($typeNode);
             }),
-            'astNode' => $def,
-            'resolveType' => [$this, 'cannotExecuteSchema']
+            'astNode' => $def
         ];
     }
 
@@ -552,17 +548,17 @@ class BuildSchema
             'name' => $def->name->value,
             'description' => $this->getDescription($def),
             'astNode' => $def,
-            'serialize' => function() {
+            '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() {
+            'parseValue' => function () {
                 return false;
             },
-            'parseLiteral' => function() {
+            'parseLiteral' => function () {
                 return false;
             }
         ];
@@ -573,7 +569,9 @@ class BuildSchema
         return [
             'name' => $def->name->value,
             'description' => $this->getDescription($def),
-            'fields' => function() use ($def) { return $this->makeInputValues($def->fields); },
+            'fields' => function () use ($def) {
+                return $this->makeInputValues($def->fields);
+            },
             'astNode' => $def,
         ];
     }
@@ -611,7 +609,7 @@ class BuildSchema
     {
         $loc = $node->loc;
         if (!$loc || !$loc->startToken) {
-            return ;
+            return;
         }
         $comments = [];
         $token = $loc->startToken->prev;
@@ -644,12 +642,4 @@ class BuildSchema
         $doc = $source instanceof DocumentNode ? $source : Parser::parse($source);
         return self::buildAST($doc, $typeConfigDecorator);
     }
-
-    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/tests/Executor/AbstractPromiseTest.php b/tests/Executor/AbstractPromiseTest.php
index 5b0f576..7652d7e 100644
--- a/tests/Executor/AbstractPromiseTest.php
+++ b/tests/Executor/AbstractPromiseTest.php
@@ -87,9 +87,7 @@ class AbstractPromiseTest extends \PHPUnit_Framework_TestCase
           }
         }';
 
-        Warning::suppress(Warning::WARNING_FULL_SCHEMA_SCAN);
         $result = GraphQL::execute($schema, $query);
-        Warning::enable(Warning::WARNING_FULL_SCHEMA_SCAN);
 
         $expected = [
             'data' => [
@@ -174,9 +172,7 @@ class AbstractPromiseTest extends \PHPUnit_Framework_TestCase
       }
     }';
 
-        Warning::suppress(Warning::WARNING_FULL_SCHEMA_SCAN);
         $result = GraphQL::execute($schema, $query);
-        Warning::enable(Warning::WARNING_FULL_SCHEMA_SCAN);
 
         $expected = [
             'data' => [
diff --git a/tests/Executor/UnionInterfaceTest.php b/tests/Executor/UnionInterfaceTest.php
index 8fc3d8a..d2b0f14 100644
--- a/tests/Executor/UnionInterfaceTest.php
+++ b/tests/Executor/UnionInterfaceTest.php
@@ -256,9 +256,7 @@ class UnionInterfaceTest extends \PHPUnit_Framework_TestCase
             ]
         ];
 
-        Warning::suppress(Warning::WARNING_FULL_SCHEMA_SCAN);
         $this->assertEquals($expected, Executor::execute($this->schema, $ast, $this->john)->toArray());
-        Warning::enable(Warning::WARNING_FULL_SCHEMA_SCAN);
     }
 
     /**
@@ -294,9 +292,7 @@ class UnionInterfaceTest extends \PHPUnit_Framework_TestCase
             ]
         ];
 
-        Warning::suppress(Warning::WARNING_FULL_SCHEMA_SCAN);
-        $this->assertEquals($expected, Executor::execute($this->schema, $ast, $this->john)->toArray());
-        Warning::enable(Warning::WARNING_FULL_SCHEMA_SCAN);
+        $this->assertEquals($expected, Executor::execute($this->schema, $ast, $this->john)->toArray(true));
     }
 
     /**
@@ -351,9 +347,7 @@ class UnionInterfaceTest extends \PHPUnit_Framework_TestCase
             ]
         ];
 
-        Warning::suppress(Warning::WARNING_FULL_SCHEMA_SCAN);
         $this->assertEquals($expected, Executor::execute($this->schema, $ast, $this->john)->toArray());
-        Warning::enable(Warning::WARNING_FULL_SCHEMA_SCAN);
     }
 
     /**
diff --git a/tests/Type/DefinitionTest.php b/tests/Type/DefinitionTest.php
index f0f3fe3..1622220 100644
--- a/tests/Type/DefinitionTest.php
+++ b/tests/Type/DefinitionTest.php
@@ -74,10 +74,7 @@ class DefinitionTest extends \PHPUnit_Framework_TestCase
 
     public function setUp()
     {
-        $this->objectType = new ObjectType([
-            'name' => 'Object',
-            'isTypeOf' => function() {return true;}
-        ]);
+        $this->objectType = new ObjectType(['name' => 'Object']);
         $this->interfaceType = new InterfaceType(['name' => 'Interface']);
         $this->unionType = new UnionType(['name' => 'Union', 'types' => [$this->objectType]]);
         $this->enumType = new EnumType(['name' => 'Enum']);
@@ -363,7 +360,6 @@ class DefinitionTest extends \PHPUnit_Framework_TestCase
                 'f' => ['type' => Type::int()]
             ],
             'interfaces' => [$someInterface],
-            'isTypeOf' => function() {return true;}
         ]);
 
         $schema = new Schema([
@@ -391,7 +387,6 @@ class DefinitionTest extends \PHPUnit_Framework_TestCase
                 'f' => ['type' => Type::int()]
             ],
             'interfaces' => function() use (&$someInterface) { return [$someInterface]; },
-            'isTypeOf' => function() {return true;}
         ]);
 
         $someInterface = new InterfaceType([
diff --git a/tests/Type/ValidationTest.php b/tests/Type/ValidationTest.php
index 2552470..6d689c6 100644
--- a/tests/Type/ValidationTest.php
+++ b/tests/Type/ValidationTest.php
@@ -58,24 +58,15 @@ class ValidationTest extends \PHPUnit_Framework_TestCase
 
         $this->ObjectWithIsTypeOf = new ObjectType([
             'name' => 'ObjectWithIsTypeOf',
-            'isTypeOf' => function() {
-                return true;
-            },
             'fields' => [ 'f' => [ 'type' => Type::string() ]]
         ]);
         $this->SomeUnionType = new UnionType([
             'name' => 'SomeUnion',
-            'resolveType' => function() {
-                return null;
-            },
             'types' => [ $this->SomeObjectType ]
         ]);
 
         $this->SomeInterfaceType = new InterfaceType([
             'name' => 'SomeInterface',
-            'resolveType' => function() {
-                return null;
-            },
             'fields' => [ 'f' => ['type' => Type::string() ]]
         ]);
 
@@ -404,7 +395,6 @@ class ValidationTest extends \PHPUnit_Framework_TestCase
     {
         $AnotherInterface = new InterfaceType([
             'name' => 'AnotherInterface',
-            'resolveType' => function() {},
             'fields' => [ 'f' => [ 'type' => Type::string() ]],
         ]);
 
@@ -736,8 +726,6 @@ class ValidationTest extends \PHPUnit_Framework_TestCase
     {
         $AnotherInterfaceType = new InterfaceType([
             'name' => 'AnotherInterface',
-            'resolveType' => function () {
-            },
             'fields' => ['f' => ['type' => Type::string()]]
         ]);
 
@@ -756,8 +744,6 @@ class ValidationTest extends \PHPUnit_Framework_TestCase
     {
         $AnotherInterfaceType = new InterfaceType([
             'name' => 'AnotherInterface',
-            'resolveType' => function () {
-            },
             'fields' => ['f' => ['type' => Type::string()]]
         ]);
 
@@ -795,14 +781,11 @@ class ValidationTest extends \PHPUnit_Framework_TestCase
     {
         $NonUniqInterface = new InterfaceType([
             'name' => 'NonUniqInterface',
-            'resolveType' => function () {
-            },
             'fields' => ['f' => ['type' => Type::string()]],
         ]);
 
         $AnotherInterface = new InterfaceType([
             'name' => 'AnotherInterface',
-            'resolveType' => function(){},
             'fields' => ['f' => ['type' => Type::string()]],
         ]);
 
@@ -851,9 +834,6 @@ class ValidationTest extends \PHPUnit_Framework_TestCase
     {
         $schema = $this->schemaWithFieldType(new UnionType([
             'name' => 'SomeUnion',
-            'resolveType' => function () {
-                return null;
-            },
             'types' => [$this->SomeObjectType],
         ]));
         $schema->assertValid();
@@ -866,9 +846,6 @@ class ValidationTest extends \PHPUnit_Framework_TestCase
     {
         $schema = $this->schemaWithFieldType(new UnionType([
             'name' => 'SomeUnion',
-            'resolveType' => function () {
-                return null;
-            },
             'types' => function () {
                 return [$this->SomeObjectType];
             },
@@ -887,7 +864,6 @@ class ValidationTest extends \PHPUnit_Framework_TestCase
         );
         $this->schemaWithFieldType(new UnionType([
             'name' => 'SomeUnion',
-            'resolveType' => function() {return null;}
         ]));
     }
 
@@ -898,8 +874,6 @@ class ValidationTest extends \PHPUnit_Framework_TestCase
     {
         $schema = $this->schemaWithFieldType(new UnionType([
             'name' => 'SomeUnion',
-            'resolveType' => function () {
-            },
             'types' => []
         ]));
 
@@ -921,8 +895,6 @@ class ValidationTest extends \PHPUnit_Framework_TestCase
         );
         $this->schemaWithFieldType(new UnionType([
             'name' => 'SomeUnion',
-            'resolveType' => function () {
-            },
             'types' => $this->SomeObjectType
         ]));
     }
@@ -934,7 +906,6 @@ class ValidationTest extends \PHPUnit_Framework_TestCase
     {
         $schema = $this->schemaWithFieldType(new UnionType([
             'name' => 'SomeUnion',
-            'resolveType' => function(){},
             'types' => [
                 $this->SomeObjectType,
                 $this->SomeObjectType,
@@ -1193,8 +1164,6 @@ class ValidationTest extends \PHPUnit_Framework_TestCase
     {
         $AnotherInterfaceType = new InterfaceType([
             'name' => 'AnotherInterface',
-            'resolveType' => function () {
-            },
             'fields' => ['f' => ['type' => Type::string()]]
         ]);
 
@@ -1234,8 +1203,6 @@ class ValidationTest extends \PHPUnit_Framework_TestCase
     {
         $AnotherInterfaceType = new InterfaceType([
             'name' => 'AnotherInterface',
-            'resolveType' => function () {
-            },
             'fields' => ['f' => ['type' => Type::string()]]
         ]);
 
@@ -1270,32 +1237,6 @@ class ValidationTest extends \PHPUnit_Framework_TestCase
         $type->assertValid();
     }
 
-    /**
-     * @it rejects an Interface type not defining resolveType with implementing type not defining isTypeOf
-     */
-    public function testRejectsAnInterfaceTypeNotDefiningResolveTypeWithImplementingTypeNotDefiningIsTypeOf()
-    {
-        $InterfaceTypeWithoutResolveType = new InterfaceType([
-            'name' => 'InterfaceTypeWithoutResolveType',
-            'fields' => ['f' => ['type' => Type::string()]]
-        ]);
-
-        $schema = $this->schemaWithFieldType(new ObjectType([
-            'name' => 'SomeObject',
-            'interfaces' => [$InterfaceTypeWithoutResolveType],
-            'fields' => ['f' => ['type' => Type::string()]]
-        ]));
-
-        $this->setExpectedException(
-            InvariantViolation::class,
-            'Interface Type InterfaceTypeWithoutResolveType does not provide a "resolveType" function and implementing '.
-            'Type SomeObject does not provide a "isTypeOf" function. There is no way to resolve this implementing type '.
-            'during execution.'
-        );
-
-        $schema->assertValid();
-    }
-
     // DESCRIBE: Type System: Union types must be resolvable
 
     /**
@@ -1305,8 +1246,6 @@ class ValidationTest extends \PHPUnit_Framework_TestCase
     {
         $schema = $this->schemaWithFieldType(new UnionType([
             'name' => 'SomeUnion',
-            'resolveType' => function () {
-            },
             'types' => [$this->SomeObjectType],
         ]));
         $schema->assertValid();
@@ -1332,8 +1271,6 @@ class ValidationTest extends \PHPUnit_Framework_TestCase
     {
         $schema = $this->schemaWithFieldType(new UnionType([
             'name' => 'SomeUnion',
-            'resolveType' => function () {
-            },
             'types' => [$this->ObjectWithIsTypeOf],
         ]));
         $schema->assertValid();
@@ -1358,25 +1295,6 @@ class ValidationTest extends \PHPUnit_Framework_TestCase
         $schema->assertValid();
     }
 
-    /**
-     * @it rejects a Union type not defining resolveType of Object types not defining isTypeOf
-     */
-    public function testRejectsAUnionTypeNotDefiningResolveTypeOfObjectTypesNotDefiningIsTypeOf()
-    {
-        $schema = $this->schemaWithFieldType(new UnionType([
-            'name' => 'SomeUnion',
-            'types' => [$this->SomeObjectType],
-        ]));
-
-        $this->setExpectedException(
-            InvariantViolation::class,
-            'Union type "SomeUnion" does not provide a "resolveType" function and possible type "SomeObject" '.
-            'does not provide an "isTypeOf" function. There is no way to resolve this possible type during execution.'
-        );
-
-        $schema->assertValid();
-    }
-
     // DESCRIBE: Type System: Scalar types must be serializable
 
     /**
@@ -1747,8 +1665,6 @@ class ValidationTest extends \PHPUnit_Framework_TestCase
     {
         $AnotherInterfaceType = new InterfaceType([
             'name' => 'AnotherInterface',
-            'resolveType' => function () {
-            },
             'fields' => ['f' => ['type' => Type::string()]]
         ]);
 
@@ -2085,8 +2001,6 @@ class ValidationTest extends \PHPUnit_Framework_TestCase
     {
         $AnotherInterface = new InterfaceType([
             'name' => 'AnotherInterface',
-            'resolveType' => function () {
-            },
             'fields' => [
                 'field' => [
                     'type' => Type::string(),
@@ -2121,8 +2035,6 @@ class ValidationTest extends \PHPUnit_Framework_TestCase
     {
         $AnotherInterface = new InterfaceType([
             'name' => 'AnotherInterface',
-            'resolveType' => function () {
-            },
             'fields' => [
                 'field' => [
                     'type' => Type::string(),
@@ -2158,8 +2070,6 @@ class ValidationTest extends \PHPUnit_Framework_TestCase
     {
         $AnotherInterface = new InterfaceType([
             'name' => 'AnotherInterface',
-            'resolveType' => function () {
-            },
             'fields' => [
                 'field' => [
                     'type' => Type::string(),
@@ -2195,8 +2105,6 @@ class ValidationTest extends \PHPUnit_Framework_TestCase
     {
         $AnotherInterface = new InterfaceType([
             'name' => 'AnotherInterface',
-            'resolveType' => function () {
-            },
             'fields' => [
                 'field' => [
                     'type' => Type::string(),
@@ -2238,8 +2146,6 @@ class ValidationTest extends \PHPUnit_Framework_TestCase
     {
         $AnotherInterface = new InterfaceType([
             'name' => 'AnotherInterface',
-            'resolveType' => function () {
-            },
             'fields' => [
                 'field' => [
                     'type' => Type::string(),
@@ -2274,8 +2180,6 @@ class ValidationTest extends \PHPUnit_Framework_TestCase
     {
         $AnotherInterface = new InterfaceType([
             'name' => 'AnotherInterface',
-            'resolveType' => function () {
-            },
             'fields' => [
                 'field' => ['type' => Type::string()]
             ]
@@ -2318,8 +2222,6 @@ class ValidationTest extends \PHPUnit_Framework_TestCase
 
         $AnotherInterface = new InterfaceType([
             'name' => 'AnotherInterface',
-            'resolveType' => function () {
-            },
             'fields' => [
                 'field' => ['type' => $TypeA]
             ]
@@ -2350,8 +2252,6 @@ class ValidationTest extends \PHPUnit_Framework_TestCase
     {
         $AnotherInterface = new InterfaceType([
             'name' => 'AnotherInterface',
-            'resolveType' => function () {
-            },
             'fields' => function () use (&$AnotherInterface) {
                 return [
                     'field' => ['type' => $AnotherInterface]
@@ -2380,8 +2280,6 @@ class ValidationTest extends \PHPUnit_Framework_TestCase
     {
         $AnotherInterface = new InterfaceType([
             'name' => 'AnotherInterface',
-            'resolveType' => function () {
-            },
             'fields' => [
                 'field' => ['type' => $this->SomeUnionType]
             ]
@@ -2406,8 +2304,6 @@ class ValidationTest extends \PHPUnit_Framework_TestCase
     {
         $AnotherInterface = new InterfaceType([
             'name' => 'AnotherInterface',
-            'resolveType' => function () {
-            },
             'fields' => [
                 'field' => [
                     'type' => Type::string(),
@@ -2445,8 +2341,6 @@ class ValidationTest extends \PHPUnit_Framework_TestCase
     {
         $AnotherInterface = new InterfaceType([
             'name' => 'AnotherInterface',
-            'resolveType' => function () {
-            },
             'fields' => [
                 'field' => [
                     'type' => Type::string(),
@@ -2487,8 +2381,6 @@ class ValidationTest extends \PHPUnit_Framework_TestCase
     {
         $AnotherInterface = new InterfaceType([
             'name' => 'AnotherInterface',
-            'resolveType' => function () {
-            },
             'fields' => [
                 'field' => ['type' => Type::nonNull(Type::listOf(Type::string()))]
             ]
@@ -2513,8 +2405,6 @@ class ValidationTest extends \PHPUnit_Framework_TestCase
     {
         $AnotherInterface = new InterfaceType([
             'name' => 'AnotherInterface',
-            'resolveType' => function () {
-            },
             'fields' => [
                 'field' => ['type' => Type::listOf(Type::string())]
             ]
@@ -2545,8 +2435,6 @@ class ValidationTest extends \PHPUnit_Framework_TestCase
     {
         $AnotherInterface = new InterfaceType([
             'name' => 'AnotherInterface',
-            'resolveType' => function () {
-            },
             'fields' => [
                 'field' => ['type' => Type::string()]
             ]
@@ -2575,8 +2463,6 @@ class ValidationTest extends \PHPUnit_Framework_TestCase
     {
         $AnotherInterface = new InterfaceType([
             'name' => 'AnotherInterface',
-            'resolveType' => function () {
-            },
             'fields' => [
                 'field' => ['type' => Type::string()]
             ]
@@ -2601,8 +2487,6 @@ class ValidationTest extends \PHPUnit_Framework_TestCase
     {
         $AnotherInterface = new InterfaceType([
             'name' => 'AnotherInterface',
-            'resolveType' => function () {
-            },
             'fields' => [
                 'field' => ['type' => Type::nonNull(Type::string())]
             ]
@@ -2820,8 +2704,6 @@ class ValidationTest extends \PHPUnit_Framework_TestCase
     {
         $BadUnionType = new UnionType([
             'name' => 'BadUnion',
-            'resolveType' => function () {
-            },
             'types' => [$type],
         ]);
         return new Schema([
diff --git a/tests/Utils/BuildSchemaTest.php b/tests/Utils/BuildSchemaTest.php
index 095f315..7f0c47e 100644
--- a/tests/Utils/BuildSchemaTest.php
+++ b/tests/Utils/BuildSchemaTest.php
@@ -36,8 +36,8 @@ class BuildSchemaTest extends \PHPUnit_Framework_TestCase
             }
         '));
 
-        $result = GraphQL::execute($schema, '{ str }', ['str' => 123]);
-        $this->assertEquals($result['data'], ['str' => 123]);
+        $result = GraphQL::executeQuery($schema, '{ str }', ['str' => 123]);
+        $this->assertEquals(['str' => 123], $result->toArray(true)['data']);
     }
 
     /**
@@ -52,7 +52,7 @@ class BuildSchemaTest extends \PHPUnit_Framework_TestCase
             }
         ");
 
-        $result = GraphQL::execute(
+        $result = GraphQL::executeQuery(
             $schema,
             '{ add(x: 34, y: 55) }',
             [
@@ -61,7 +61,7 @@ class BuildSchemaTest extends \PHPUnit_Framework_TestCase
                 }
             ]
         );
-        $this->assertEquals($result, ['data' => ['add' => 89]]);
+        $this->assertEquals(['data' => ['add' => 89]], $result->toArray(true));
     }
 
     /**
@@ -447,6 +447,135 @@ type WorldTwo {
         $this->assertEquals($output, $body);
     }
 
+    /**
+     * @it Specifying Union type using __typename
+     */
+    public function testSpecifyingUnionTypeUsingTypename()
+    {
+        $schema = BuildSchema::buildAST(Parser::parse('
+            schema {
+              query: Root
+            }
+            
+            type Root {
+              fruits: [Fruit]
+            }
+            
+            union Fruit = Apple | Banana
+            
+            type Apple {
+              color: String
+            }
+            
+            type Banana {
+              length: Int
+            }
+        '));
+        $query = '
+            {
+              fruits {
+                ... on Apple {
+                  color
+                }
+                ... on Banana {
+                  length
+                }
+              }
+            }
+        ';
+        $root = [
+            'fruits' => [
+                [
+                    'color' => 'green',
+                    '__typename' => 'Apple',
+                ],
+                [
+                    'length' => 5,
+                    '__typename' => 'Banana',
+                ]
+            ]
+        ];
+        $expected = [
+            'data' => [
+                'fruits' => [
+                    ['color' => 'green'],
+                    ['length' => 5],
+                ]
+            ]
+        ];
+
+        $result = GraphQL::executeQuery($schema, $query, $root);
+        $this->assertEquals($expected, $result->toArray(true));
+    }
+
+    /**
+     * @it Specifying Interface type using __typename
+     */
+    public function testSpecifyingInterfaceUsingTypename()
+    {
+        $schema = BuildSchema::buildAST(Parser::parse('
+            schema {
+              query: Root
+            }
+            
+            type Root {
+              characters: [Character]
+            }
+            
+            interface Character {
+              name: String!
+            }
+            
+            type Human implements Character {
+              name: String!
+              totalCredits: Int
+            }
+            
+            type Droid implements Character {
+              name: String!
+              primaryFunction: String
+            }
+        '));
+        $query = '
+            {
+              characters {
+                name
+                ... on Human {
+                  totalCredits
+                }
+                ... on Droid {
+                  primaryFunction
+                }
+              }
+            }
+        ';
+        $root = [
+            'characters' => [
+                [
+                    'name' => 'Han Solo',
+                    'totalCredits' => 10,
+                    '__typename' => 'Human',
+                ],
+                [
+                    'name' => 'R2-D2',
+                    'primaryFunction' => 'Astromech',
+                    '__typename' => 'Droid',
+                ]
+            ]
+        ];
+        $expected = [
+            'data' => [
+                'characters' => [
+                    ['name' => 'Han Solo', 'totalCredits' => 10],
+                    ['name' => 'R2-D2', 'primaryFunction' => 'Astromech'],
+                ]
+            ]
+        ];
+
+        $result = GraphQL::executeQuery($schema, $query, $root);
+        $this->assertEquals($expected, $result->toArray(true));
+    }
+
     /**
      * @it CustomScalar
      */
@@ -1093,9 +1222,8 @@ interface Hello {
         $this->assertInstanceOf(InterfaceTypeDefinitionNode::class, $node);
         $this->assertEquals('Hello', $defaultConfig['name']);
         $this->assertInstanceOf(\Closure::class, $defaultConfig['fields']);
-        $this->assertInstanceOf(\Closure::class, $defaultConfig['resolveType']);
         $this->assertArrayHasKey('description', $defaultConfig);
-        $this->assertCount(5, $defaultConfig);
+        $this->assertCount(4, $defaultConfig);
         $this->assertEquals(array_keys($allNodesMap), ['Query', 'Color', 'Hello']);
         $this->assertEquals('My description of Hello', $schema->getType('Hello')->description);
     }
diff --git a/tests/Utils/FindBreakingChangesTest.php b/tests/Utils/FindBreakingChangesTest.php
index 2fc0f6f..b48f961 100644
--- a/tests/Utils/FindBreakingChangesTest.php
+++ b/tests/Utils/FindBreakingChangesTest.php
@@ -1,8 +1,4 @@
 <?php
-/**
- * FindBreakingChanges tests
- */
-
 namespace GraphQL\Tests\Utils;
 
 use GraphQL\Type\Definition\EnumType;
@@ -16,7 +12,6 @@ use GraphQL\Utils\FindBreakingChanges;
 
 class FindBreakingChangesTest extends \PHPUnit_Framework_TestCase
 {
-
     private $queryType;
 
     public function setUp()
@@ -88,7 +83,7 @@ class FindBreakingChangesTest extends \PHPUnit_Framework_TestCase
 
         $unionType = new UnionType([
             'name' => 'Type1',
-            'types' => [new ObjectType(['name' => 'blah'])],
+            'types' => [$objectType],
         ]);
 
         $oldSchema = new Schema([
@@ -510,16 +505,12 @@ class FindBreakingChangesTest extends \PHPUnit_Framework_TestCase
         $oldUnionType = new UnionType([
             'name' => 'UnionType1',
             'types' => [$type1, $type2],
-            'resolveType' => function () {
-            }
         ]);
 
 
         $newUnionType = new UnionType([
             'name' => 'UnionType1',
             'types' => [$type1a, $type3],
-            'resolveType' => function () {
-            }
         ]);
 
         $oldSchema = new Schema([
@@ -978,8 +969,6 @@ class FindBreakingChangesTest extends \PHPUnit_Framework_TestCase
             'fields' => [
                 'field1' => Type::string()
             ],
-            'resolveType' => function () {
-            }
         ]);
         $oldType = new ObjectType([
             'name' => 'Type1',
@@ -1099,15 +1088,11 @@ class FindBreakingChangesTest extends \PHPUnit_Framework_TestCase
         $unionTypeThatLosesATypeOld = new UnionType([
             'name' => 'UnionTypeThatLosesAType',
             'types' => [$typeInUnion1, $typeInUnion2],
-            'resolveType' => function () {
-            }
         ]);
 
         $unionTypeThatLosesATypeNew = new UnionType([
             'name' => 'UnionTypeThatLosesAType',
             'types' => [$typeInUnion1],
-            'resolveType' => function () {
-            }
         ]);
 
         $enumTypeThatLosesAValueOld = new EnumType([
@@ -1132,8 +1117,6 @@ class FindBreakingChangesTest extends \PHPUnit_Framework_TestCase
             'fields' => [
                 'field1' => Type::string()
             ],
-            'resolveType' => function () {
-            }
         ]);
 
         $typeThatLosesInterfaceOld = new ObjectType([
@@ -1353,15 +1336,11 @@ class FindBreakingChangesTest extends \PHPUnit_Framework_TestCase
         $oldUnionType = new UnionType([
             'name' => 'UnionType1',
             'types' => [$type1],
-            'resolveType' => function () {
-            }
         ]);
 
         $newUnionType = new UnionType([
             'name' => 'UnionType1',
             'types' => [$type1a, $type2],
-            'resolveType' => function () {
-            }
         ]);
 
         $oldSchema = new Schema([
@@ -1452,15 +1431,11 @@ class FindBreakingChangesTest extends \PHPUnit_Framework_TestCase
         $unionTypeThatGainsATypeOld = new UnionType([
             'name' => 'UnionType1',
             'types' => [$typeInUnion1],
-            'resolveType' => function () {
-            }
         ]);
 
         $unionTypeThatGainsATypeNew = new UnionType([
             'name' => 'UnionType1',
             'types' => [$typeInUnion1, $typeInUnion2],
-            'resolveType' => function () {
-            }
         ]);
 
         $oldSchema = new Schema([
@@ -1498,4 +1473,4 @@ class FindBreakingChangesTest extends \PHPUnit_Framework_TestCase
 
         $this->assertEquals($expectedDangerousChanges, FindBreakingChanges::findDangerousChanges($oldSchema, $newSchema));
     }
-}
\ No newline at end of file
+}
diff --git a/tests/Utils/SchemaPrinterTest.php b/tests/Utils/SchemaPrinterTest.php
index 0acf0c2..5dac505 100644
--- a/tests/Utils/SchemaPrinterTest.php
+++ b/tests/Utils/SchemaPrinterTest.php
@@ -360,7 +360,6 @@ type Root {
     {
         $fooType = new InterfaceType([
             'name' => 'Foo',
-            'resolveType' => function() { return null; },
             'fields' => ['str' => ['type' => Type::string()]]
         ]);
 
@@ -406,13 +405,11 @@ type Root {
     {
         $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()]]
         ]);
 
@@ -476,13 +473,11 @@ type Root {
 
         $singleUnion = new UnionType([
             'name' => 'SingleUnion',
-            'resolveType' => function() { return null; },
             'types' => [$fooType]
         ]);
 
         $multipleUnion = new UnionType([
             'name' => 'MultipleUnion',
-            'resolveType' => function() { return null; },
             'types' => [$fooType, $barType]
         ]);
 
@@ -1098,4 +1093,4 @@ enum __TypeKind {
 EOT;
         $this->assertEquals($introspectionSchema, $output);
     }
-}
\ No newline at end of file
+}
diff --git a/tests/Validator/OverlappingFieldsCanBeMergedTest.php b/tests/Validator/OverlappingFieldsCanBeMergedTest.php
index 48d3053..c9900e7 100644
--- a/tests/Validator/OverlappingFieldsCanBeMergedTest.php
+++ b/tests/Validator/OverlappingFieldsCanBeMergedTest.php
@@ -795,7 +795,6 @@ class OverlappingFieldsCanBeMergedTest extends TestCase
 
         $SomeBox = new InterfaceType([
             'name' => 'SomeBox',
-            'resolveType' => function() use (&$StringBox) {return $StringBox;},
             'fields' => function() use (&$SomeBox) {
                 return [
                     'deepBox' => ['type' => $SomeBox],
@@ -837,7 +836,6 @@ class OverlappingFieldsCanBeMergedTest extends TestCase
 
         $NonNullStringBox1 = new InterfaceType([
             'name' => 'NonNullStringBox1',
-            'resolveType' => function() use (&$StringBox) {return $StringBox;},
             'fields' => [
                 'scalar' => [ 'type' => Type::nonNull(Type::string()) ]
             ]
@@ -855,7 +853,6 @@ class OverlappingFieldsCanBeMergedTest extends TestCase
 
         $NonNullStringBox2 = new InterfaceType([
             'name' => 'NonNullStringBox2',
-            'resolveType' => function() use (&$StringBox) {return $StringBox;},
             'fields' => [
                 'scalar' => ['type' => Type::nonNull(Type::string())]
             ]
diff --git a/tests/Validator/TestCase.php b/tests/Validator/TestCase.php
index 387012a..c96a08d 100644
--- a/tests/Validator/TestCase.php
+++ b/tests/Validator/TestCase.php
@@ -67,7 +67,6 @@ abstract class TestCase extends \PHPUnit_Framework_TestCase
 
         $Dog = new ObjectType([
             'name' => 'Dog',
-            'isTypeOf' => function() {return true;},
             'fields' => [
                 'name' => [
                     'type' => Type::string(),
@@ -94,7 +93,6 @@ abstract class TestCase extends \PHPUnit_Framework_TestCase
 
         $Cat = new ObjectType([
             'name' => 'Cat',
-            'isTypeOf' => function() {return true;},
             'fields' => function() use (&$FurColor) {
                 return [
                     'name' => [
@@ -113,10 +111,6 @@ abstract class TestCase extends \PHPUnit_Framework_TestCase
         $CatOrDog = new UnionType([
             'name' => 'CatOrDog',
             'types' => [$Dog, $Cat],
-            'resolveType' => function($value) {
-                // not used for validation
-                return null;
-            }
         ]);
 
         $Intelligent = new InterfaceType([
@@ -129,7 +123,6 @@ abstract class TestCase extends \PHPUnit_Framework_TestCase
         $Human = null;
         $Human = new ObjectType([
             'name' => 'Human',
-            'isTypeOf' => function() {return true;},
             'interfaces' => [$Being, $Intelligent],
             'fields' => function() use (&$Human, $Pet) {
                 return [
@@ -146,7 +139,6 @@ abstract class TestCase extends \PHPUnit_Framework_TestCase
 
         $Alien = new ObjectType([
             'name' => 'Alien',
-            'isTypeOf' => function() {return true;},
             'interfaces' => [$Being, $Intelligent],
             'fields' => [
                 'iq' => ['type' => Type::int()],
@@ -161,19 +153,11 @@ abstract class TestCase extends \PHPUnit_Framework_TestCase
         $DogOrHuman = new UnionType([
             'name' => 'DogOrHuman',
             'types' => [$Dog, $Human],
-            'resolveType' => function() {
-                // not used for validation
-                return null;
-            }
         ]);
 
         $HumanOrAlien = new UnionType([
             'name' => 'HumanOrAlien',
             'types' => [$Human, $Alien],
-            'resolveType' => function() {
-                // not used for validation
-                return null;
-            }
         ]);
 
         $FurColor = new EnumType([