The principal changes introduced in Joomla 2.5.x are:
- New Access Control System - Allows site administrators control over who can view and manage content.
- Unlimited Depth Organizational Model - Gives site administrators and content creators user-defined category levels that allow for the creation of a category tree with as many or as few levels for organizing articles and other content as needed.
- One-Click Extension Updates - Allows users to keep sites secure and controlled by simplifying the process of updating extensions.
- Semantic XHTML Layouts - Provides a better baseline for content presentation.
The following is a more complete list of changes.