TYPO3 is a web content management system (CMS) written in the programming language PHP. It is free and open-source software released under the GNU General Public License version 2.

TYPO3 is similar to other content management systems such as Drupal, Joomla!, and WordPress. It is used more widely in Europe than in other regions, with a larger market share in German-speaking countries, the Netherlands, and France.^[2][3][4]

TYPO3 allows for the separate maintenance of code and content. It can be extended with new functions without writing any program code. TYPO3 supports publishing content in multiple languages due to its built-in localization system.

TYPO3 was initially authored by Kasper Skårhøj in 1997.^[5] It is now developed by over 300 contributors under the lead of Benjamin Mack.^[6]

Calculations from the TYPO3 Association show that it is currently used in more than 500,000 installations. The number of installations detected by the public website "CMS Crawler" was around 384,000 in February 2017.^[3][7]

TYPO3 provides a base set of interfaces, functions and modules. Most functionality exceeding the base set can be implemented via the use of extensions. More than 5000 extensions are currently available for TYPO3 for download under the GNU General Public License from a repository called the TYPO3 Extension Repository, or TER.^[8]