The Joomla package consists of many different parts, which are built to be as modular as possible, allowing extensions and integrations to be made easily. An example of such are extensions called "Plugins".(Previously known as "Mambots".) Plugins are background extensions that extend Joomla with new functionality. The WikiBot, for example, allows the author of Joomla content to use "Wikitags" in Joomla articles which will auto-create dynamic hyperlinks to Wikipedia articles when displayed. There are over 2,300 extensions for Joomla available via the Extensions Directory, a site that OpenSourceMatters runs as an official directory of extensions.

In addition to Plugins, more comprehensive extensions are available. "Components" allow webmasters to perform such tasks as build a community by expanding user features, backup a website, translate content and create URLS that are more friendly to search engines. "Modules" perform such tasks as displaying a calendar or allowing custom code like Google AdSense etc to be inserted within the base Joomla code.