The ClassLoader Component loads your project classes automatically if they follow some standard PHP conventions. Whenever you use an undefined class, PHP uses the auto-loading mechanism to delegate the loading of a file defining the class. Symfony2 provides a "universal" auto-loader, which is able to load classes from files that implement one of the following conventions: * The technical interoperability standards for PHP 5.3 name-spaces and class names. * The PEAR naming convention for classes. If your classes and the third-party libraries you use for your project follow these standards, the Symfony2 auto-loader is the only auto-loader you will ever need. Optional dependencies: APC, XCache