diff --git a/phpBB/includes/class_loader.php b/phpBB/includes/class_loader.php
new file mode 100644
index 0000000000..c70351b437
--- /dev/null
+++ b/phpBB/includes/class_loader.php
@@ -0,0 +1,162 @@
+<?php
+/**
+*
+* @package phpBB3
+* @version $Id$
+* @copyright (c) 2005 phpBB Group
+* @license http://opensource.org/licenses/gpl-license.php GNU Public License
+*
+*/
+
+/**
+* @ignore
+*/
+if (!defined('IN_PHPBB'))
+{
+	exit;
+}
+
+/**
+* The class loader resolves class names to file system paths and loads them if
+* necessary.
+*
+* Classes have to be of the form phpbb_(dir_)*(classpart_)*, so directory names
+* must never contain underscores. Example: phpbb_dir_subdir_class_name is a
+* valid class name, while phpbb_dir_sub_dir_class_name is not.
+*
+* If every part of the class name is a directory, the last directory name is
+* also used as the filename, e.g. phpbb_dir would resolve to dir/dir.php.
+*
+* @package phpBB3
+*/
+class phpbb_class_loader
+{
+	private $phpbb_root_path;
+	private $php_ext;
+	private $cache;
+	private $cached_paths = array();
+
+	/**
+	* Creates a new phpbb_class_loader, which loads files with the given
+	* file extension from the given phpbb root path.
+	*
+	* @param string $phpbb_root_path phpBB's root directory containing includes/
+	* @param string $php_ext         The file extension for PHP files
+	*/
+	public function __construct($phpbb_root_path, $php_ext = '.php', $cache = null)
+	{
+		$this->phpbb_root_path = $phpbb_root_path;
+		$this->php_ext = $php_ext;
+
+		$this->set_cache($cache);
+	}
+
+	/**
+	* Provide the class loader with a cache to store paths. If set to null, the
+	* the class loader will resolve paths by checking for the existance of every
+	* directory in the class name every time.
+	*
+	* @param acm $cache An implementation of the phpBB cache interface.
+	*/
+	public function set_cache($cache = null)
+	{
+		if ($cache)
+		{
+			$this->cached_paths = $cache->get('class_loader');
+
+			if ($this->cached_paths === false)
+			{
+				$this->cached_paths = array();
+			}
+		}
+
+		$this->cache = $cache;
+	}
+
+	/**
+	* Registers the class loader as an autoloader using SPL.
+	*/
+	public function register()
+	{
+		spl_autoload_register(array($this, 'load_class'));
+	}
+
+	/**
+	* Removes the class loader from the SPL autoloader stack.
+	*/
+	public function unregister()
+	{
+		spl_autoload_unregister(array($this, 'load_class'));
+	}
+
+	/**
+	* Resolves a phpBB class name to a relative path which can be included.
+	*
+	* @param string       $class The class name to resolve, must have a phpbb_
+	*                            prefix
+	* @return string|bool        A relative path to the file containing the
+	*                            class or false if looking it up failed.
+	*/
+	public function resolve_path($class)
+	{
+		$path_prefix = $this->phpbb_root_path . 'includes/';
+
+		if (isset($this->cached_paths[$class]))
+		{
+			return $path_prefix . $this->cached_paths[$class] . $this->php_ext;
+		}
+
+		if (!preg_match('/phpbb_[a-zA-Z0-9_]+/', $class))
+		{
+			return false;
+		}
+
+		$parts = explode('_', substr($class, 6));
+
+		$dirs = '';
+
+		for ($i = 0; is_dir($path_prefix . $dirs . $parts[$i]) && $i < sizeof($parts); $i++)
+		{
+			$dirs .= $parts[$i] . '/';
+		}
+
+		// no file name left => use last dir name as file name
+		if ($i == sizeof($parts))
+		{
+			$parts[] = $parts[$i - 1];
+		}
+
+		$relative_path = $dirs . implode(array_slice($parts, $i, sizeof($parts) - $i), '_');
+
+		if (!file_exists($path_prefix . $relative_path . $this->php_ext))
+		{
+			return false;
+		}
+
+		if ($this->cache)
+		{
+			$this->cached_paths[$class] = $relative_path;
+			$this->cache->put('class_loader', $this->cached_paths);
+		}
+
+		return $path_prefix . $relative_path . $this->php_ext;
+	}
+
+	/**
+	* Resolves a class name to a path and then includes it.
+	*
+	* @param string $class The class name which is being loaded.
+	*/
+	public function load_class($class)
+	{
+		if (substr($class, 0, 6) === 'phpbb_')
+		{
+			$path = $this->resolve_path($class);
+
+			if ($path)
+			{
+				require $path;
+			}
+		}
+	}
+}
diff --git a/tests/all_tests.php b/tests/all_tests.php
index 938b17cf26..4eee950860 100644
--- a/tests/all_tests.php
+++ b/tests/all_tests.php
@@ -15,6 +15,7 @@ if (!defined('PHPUnit_MAIN_METHOD'))
 require_once 'test_framework/framework.php';
 require_once 'PHPUnit/TextUI/TestRunner.php';
 
+require_once 'class_loader/all_tests.php';
 require_once 'utf/all_tests.php';
 require_once 'request/all_tests.php';
 require_once 'security/all_tests.php';
@@ -38,6 +39,7 @@ class phpbb_all_tests
 	{
 		$suite = new PHPUnit_Framework_TestSuite('phpBB');
 
+		$suite->addTest(phpbb_class_loader_all_tests::suite());
 		$suite->addTest(phpbb_utf_all_tests::suite());
 		$suite->addTest(phpbb_request_all_tests::suite());
 		$suite->addTest(phpbb_security_all_tests::suite());
diff --git a/tests/class_loader/all_tests.php b/tests/class_loader/all_tests.php
new file mode 100644
index 0000000000..451a1b02c2
--- /dev/null
+++ b/tests/class_loader/all_tests.php
@@ -0,0 +1,41 @@
+<?php
+/**
+*
+* @package testing
+* @copyright (c) 2008 phpBB Group
+* @license http://opensource.org/licenses/gpl-license.php GNU Public License
+*
+*/
+
+if (!defined('PHPUnit_MAIN_METHOD'))
+{
+	define('PHPUnit_MAIN_METHOD', 'phpbb_class_loader_all_tests::main');
+}
+
+require_once 'test_framework/framework.php';
+require_once 'PHPUnit/TextUI/TestRunner.php';
+
+require_once 'class_loader/class_loader_test.php';
+
+class phpbb_class_loader_all_tests
+{
+	public static function main()
+	{
+		PHPUnit_TextUI_TestRunner::run(self::suite());
+	}
+
+	public static function suite()
+	{
+		$suite = new PHPUnit_Framework_TestSuite('phpBB Class Loader');
+
+		$suite->addTestSuite('phpbb_class_loader_test');
+
+		return $suite;
+	}
+}
+
+if (PHPUnit_MAIN_METHOD == 'phpbb_class_loader_all_tests::main')
+{
+	phpbb_class_loader_all_tests::main();
+}
+
diff --git a/tests/class_loader/cache_mock.php b/tests/class_loader/cache_mock.php
new file mode 100644
index 0000000000..c8069fa9cc
--- /dev/null
+++ b/tests/class_loader/cache_mock.php
@@ -0,0 +1,29 @@
+<?php
+/**
+*
+* @package testing
+* @version $Id$
+* @copyright (c) 2008 phpBB Group
+* @license http://opensource.org/licenses/gpl-license.php GNU Public License
+*
+*/
+
+class phpbb_cache_mock
+{
+	private $variables = array();
+
+	function get($var_name)
+	{
+		if (isset($this->variables[$var_name]))
+		{
+			return $this->variables[$var_name];
+		}
+
+		return false;
+	}
+
+	function put($var_name, $value)
+	{
+		$this->variables[$var_name] = $value;
+	}
+}
\ No newline at end of file
diff --git a/tests/class_loader/class_loader_test.php b/tests/class_loader/class_loader_test.php
new file mode 100644
index 0000000000..37c11657c4
--- /dev/null
+++ b/tests/class_loader/class_loader_test.php
@@ -0,0 +1,65 @@
+<?php
+/**
+*
+* @package testing
+* @version $Id$
+* @copyright (c) 2008 phpBB Group
+* @license http://opensource.org/licenses/gpl-license.php GNU Public License
+*
+*/
+
+require_once 'test_framework/framework.php';
+require_once 'class_loader/cache_mock.php';
+
+require_once '../phpBB/includes/class_loader.php';
+
+
+class phpbb_class_loader_test extends PHPUnit_Framework_TestCase
+{
+	public function test_resolve_path()
+	{
+		$prefix = 'class_loader/';
+		$class_loader = new phpbb_class_loader($prefix);
+
+		$prefix .= 'includes/';
+
+		$this->assertEquals(
+			$prefix . 'class_name.php',
+			$class_loader->resolve_path('phpbb_class_name'),
+			'Top level class'
+		);
+		$this->assertEquals(
+			$prefix . 'dir/class_name.php',
+			$class_loader->resolve_path('phpbb_dir_class_name'),
+			'Class in a directory'
+		);
+		$this->assertEquals(
+			$prefix . 'dir/subdir/class_name.php',
+			$class_loader->resolve_path('phpbb_dir_subdir_class_name'),
+			'Class in a sub-directory'
+		);
+	}
+
+	public function test_resolve_cached()
+	{
+		$cache = new phpbb_cache_mock;
+		$cache->put('class_loader', array('phpbb_a_cached_name' => 'a/cached_name'));
+
+		$prefix = 'class_loader/';
+		$class_loader = new phpbb_class_loader($prefix, '.php', $cache);
+
+		$prefix .= 'includes/';
+
+		$this->assertEquals(
+			$prefix . 'dir/class_name.php',
+			$class_loader->resolve_path('phpbb_dir_class_name'),
+			'Class in a directory'
+		);
+
+		$this->assertEquals(
+			$prefix . 'a/cached_name.php',
+			$class_loader->resolve_path('phpbb_a_cached_name'),
+			'Class in a directory'
+		);
+	}
+}
diff --git a/tests/class_loader/includes/class_name.php b/tests/class_loader/includes/class_name.php
new file mode 100644
index 0000000000..e941173cdd
--- /dev/null
+++ b/tests/class_loader/includes/class_name.php
@@ -0,0 +1,6 @@
+<?php
+
+class phpbb_class_name
+{
+}
+
diff --git a/tests/class_loader/includes/dir/class_name.php b/tests/class_loader/includes/dir/class_name.php
new file mode 100644
index 0000000000..0675aa8fc5
--- /dev/null
+++ b/tests/class_loader/includes/dir/class_name.php
@@ -0,0 +1,6 @@
+<?php
+
+class phpbb_dir_class_name
+{
+}
+
diff --git a/tests/class_loader/includes/dir/subdir/class_name.php b/tests/class_loader/includes/dir/subdir/class_name.php
new file mode 100644
index 0000000000..7321a609cc
--- /dev/null
+++ b/tests/class_loader/includes/dir/subdir/class_name.php
@@ -0,0 +1,6 @@
+<?php
+
+class phpbb_dir_subdir_class_name
+{
+}
+