diff --git a/Classes/PHPExcel/Calculation.php b/Classes/PHPExcel/Calculation.php
index 0e6e230..a3f7be2 100644
--- a/Classes/PHPExcel/Calculation.php
+++ b/Classes/PHPExcel/Calculation.php
@@ -841,7 +841,7 @@ class PHPExcel_Calculation {
 												 'argumentCount'	=>	'1,2'
 												),
 				'HLOOKUP'				=> array('category'			=>	PHPExcel_Calculation_Function::CATEGORY_LOOKUP_AND_REFERENCE,
-												 'functionCall'		=>	'PHPExcel_Calculation_Functions::DUMMY',
+												 'functionCall'		=>	'PHPExcel_Calculation_LookupRef::HLOOKUP',
 												 'argumentCount'	=>	'3,4'
 												),
 				'HOUR'					=> array('category'			=>	PHPExcel_Calculation_Function::CATEGORY_DATE_AND_TIME,
diff --git a/Classes/PHPExcel/Calculation/LookupRef.php b/Classes/PHPExcel/Calculation/LookupRef.php
index 96f6020..c3a3f07 100644
--- a/Classes/PHPExcel/Calculation/LookupRef.php
+++ b/Classes/PHPExcel/Calculation/LookupRef.php
@@ -721,7 +721,8 @@ class PHPExcel_Calculation_LookupRef {
 
 		$rowNumber = $rowValue = False;
 		foreach($lookup_array as $rowKey => $rowData) {
-			if (strtolower($rowData[$firstColumn]) > strtolower($lookup_value)) {
+			if ((is_numeric($lookup_value) && is_numeric($rowData[$firstColumn]) && ($rowData[$firstColumn] > $lookup_value)) ||
+				(!is_numeric($lookup_value) && !is_numeric($rowData[$firstColumn]) && (strtolower($rowData[$firstColumn]) > strtolower($lookup_value)))) {
 				break;
 			}
 			$rowNumber = $rowKey;
@@ -742,6 +743,69 @@ class PHPExcel_Calculation_LookupRef {
 	}	//	function VLOOKUP()
 
 
+/**
+    * HLOOKUP
+    * The HLOOKUP function searches for value in the top-most row of lookup_array and returns the value in the same column based on the index_number.
+    * @param    lookup_value    The value that you want to match in lookup_array
+    * @param    lookup_array    The range of cells being searched
+    * @param    index_number    The row number in table_array from which the matching value must be returned. The first row is 1.
+    * @param    not_exact_match Determines if you are looking for an exact match based on lookup_value.
+    * @return   mixed           The value of the found cell
+    */
+    public static function HLOOKUP($lookup_value, $lookup_array, $index_number, $not_exact_match=true) {
+        $lookup_value   = PHPExcel_Calculation_Functions::flattenSingleValue($lookup_value);
+        $index_number   = PHPExcel_Calculation_Functions::flattenSingleValue($index_number);
+        $not_exact_match    = PHPExcel_Calculation_Functions::flattenSingleValue($not_exact_match);
+
+        // index_number must be greater than or equal to 1
+        if ($index_number < 1) {
+            return PHPExcel_Calculation_Functions::VALUE();
+        }
+
+        // index_number must be less than or equal to the number of columns in lookup_array
+        if ((!is_array($lookup_array)) || (empty($lookup_array))) {
+            return PHPExcel_Calculation_Functions::REF();
+        } else {
+            $f = array_keys($lookup_array);
+            $firstRow = array_pop($f);
+            if ((!is_array($lookup_array[$firstRow])) || ($index_number > count($lookup_array[$firstRow]))) {
+                return PHPExcel_Calculation_Functions::REF();
+            } else {
+                $columnKeys = array_keys($lookup_array[$firstRow]);
+                                $firstkey = $f[0] - 1;
+                $returnColumn = $firstkey + $index_number;
+                $firstColumn = array_shift($f);
+            }
+        }
+
+        if (!$not_exact_match) {
+            $firstRowH = asort($lookup_array[$firstColumn]);
+        }
+
+        $rowNumber = $rowValue = False;
+        foreach($lookup_array[$firstColumn] as $rowKey => $rowData) {
+			if ((is_numeric($lookup_value) && is_numeric($rowData) && ($rowData > $lookup_value)) ||
+				(!is_numeric($lookup_value) && !is_numeric($rowData) && (strtolower($rowData) > strtolower($lookup_value)))) {
+                break;
+            }
+            $rowNumber = $rowKey;
+            $rowValue = $rowData;
+        }
+
+        if ($rowNumber !== false) {
+            if ((!$not_exact_match) && ($rowValue != $lookup_value)) {
+                //  if an exact match is required, we have what we need to return an appropriate response
+                return PHPExcel_Calculation_Functions::NA();
+            } else {
+                //  otherwise return the appropriate value
+                return $lookup_array[$returnColumn][$rowNumber];
+            }
+        }
+
+        return PHPExcel_Calculation_Functions::NA();
+    }   //  function HLOOKUP()
+
+
 	/**
 	 * LOOKUP
 	 * The LOOKUP function searches for value either from a one-row or one-column range or from an array.
diff --git a/changelog.txt b/changelog.txt
index 4847b08..3c27a1b 100644
--- a/changelog.txt
+++ b/changelog.txt
@@ -23,6 +23,12 @@
 **************************************************************************************
 
 
+Fixed in develop branch for release v1.7.9a:
+- Bugfix:   (MBaker)    Work item 19830  - Undefined variable: fileHandle in CSV Reader
+- Bugfix:   (MBaker)                     - Style error with merged cells in PDF Writer
+- Bugfix:   (MBaker)                     - Problem with cloning worksheets
+- Feature:  (amerov)                     - Implementation of the Excel HLOOKUP() function
+
 Fixed in develop branch for release v1.7.9:
 - Feature:  (MBaker)    Include charts option for HTML Writer
 - Feature:  (MBaker)    Added composer file
diff --git a/unitTests/Classes/PHPExcel/Calculation/LookupRefTest.php b/unitTests/Classes/PHPExcel/Calculation/LookupRefTest.php
new file mode 100644
index 0000000..bc63431
--- /dev/null
+++ b/unitTests/Classes/PHPExcel/Calculation/LookupRefTest.php
@@ -0,0 +1,34 @@
+<?php
+
+
+require_once 'testDataFileIterator.php';
+
+class LookupRefTest extends PHPUnit_Framework_TestCase
+{
+
+    public function setUp()
+    {
+        if (!defined('PHPEXCEL_ROOT'))
+        {
+            define('PHPEXCEL_ROOT', APPLICATION_PATH . '/');
+        }
+        require_once(PHPEXCEL_ROOT . 'PHPExcel/Autoloader.php');
+	}
+
+    /**
+     * @dataProvider providerHLOOKUP
+     */
+	public function testHLOOKUP()
+	{
+		$args = func_get_args();
+		$expectedResult = array_pop($args);
+		$result = call_user_func_array(array('PHPExcel_Calculation_LookupRef','HLOOKUP'),$args);
+		$this->assertEquals($expectedResult, $result);
+	}
+
+    public function providerHLOOKUP()
+    {
+    	return new testDataFileIterator('rawTestData/Calculation/LookupRef/HLOOKUP.data');
+	}
+
+}
diff --git a/unitTests/rawTestData/Calculation/LookupRef/HLOOKUP.data b/unitTests/rawTestData/Calculation/LookupRef/HLOOKUP.data
new file mode 100644
index 0000000..c29fdc9
--- /dev/null
+++ b/unitTests/rawTestData/Calculation/LookupRef/HLOOKUP.data
@@ -0,0 +1,9 @@
+10251,		{"Order ID"|10247|10249|10250|10251|10252|10253;"Unit Price"|14.00|18.60|7.70|16.80|16.80|64.80;"Quantity"|12|9|10|6|20|40},	2,	FALSE,	16.8
+10251,		{"Order ID"|10247|10249|10250|10251|10252|10253;"Unit Price"|14.00|18.60|7.70|16.80|16.80|64.80;"Quantity"|12|9|10|6|20|40},	3,	FALSE,	6.0
+10248,		{"Order ID"|10247|10249|10250|10251|10252|10253;"Unit Price"|14.00|18.60|7.70|16.80|16.80|64.80;"Quantity"|12|9|10|6|20|40},	2,	FALSE,	"#N/A"
+10248,		{"Order ID"|10247|10249|10250|10251|10252|10253;"Unit Price"|14.00|18.60|7.70|16.80|16.80|64.80;"Quantity"|12|9|10|6|20|40},	2,	TRUE,	14.0
+"Axles",	{"Axles"|"Bearings"|"Bolts";4|4|9;5|7|10;6|8|11},																				2,	TRUE,	4
+"Bearings",	{"Axles"|"Bearings"|"Bolts";4|4|9;5|7|10;6|8|11},																				3,	FALSE,	7
+"B",		{"Axles"|"Bearings"|"Bolts";4|4|9;5|7|10;6|8|11},																				3,	TRUE,	5
+"Bolts",	{"Axles"|"Bearings"|"Bolts";4|4|9;5|7|10;6|8|11},																				4,			11
+3,			{1|2|3;"a"|"b"|"c";"d"|"e"|"f"},																								2,	TRUE,	"c"