In this introductory chapter, we first understood the need for extending Joomla! 1.5 and compared customization with extension. We learnt that Joomla! can be extended through components, modules, and plug-ins. This allows you to add functionality to a Joomla! site without hacking the core code. Joomla! can then be maintained and updated without disturbing the custom code. We also saw an overview of the topics that we will be covering in the chapters that follow.