MediaWiki is open-source wiki software written in PHP, originally developed in 2002 to power Wikipedia. It now underpins all Wikimedia Foundation projects — including Wiktionary, Wikimedia Commons, and Wikidata — and is widely used elsewhere, from public wikis like Fandom and wikiHow to internal government systems such as the US Intelligence Community's Intellipedia and the State Department's Diplopedia.
Built to handle massive scale, it supports terabytes of content and hundreds of thousands of page views per second through multi-layer caching and database replication. Its interface is available in over 400 languages, and administrators have access to hundreds of configuration settings and more than 1,000 extensions.
Core features include a lightweight wiki markup language (with an optional WYSIWYG editor, VisualEditor), a robust version history and edit-tracking system, a web API supporting bots and third-party tools, flexible user permissions, namespaces, categories, templates, and powerful search integration via Elasticsearch. Extensions can add everything from citation formatting and mathematical rendering to spam prevention and semantic data querying.
MediaWiki stores content in MySQL/MariaDB, PostgreSQL, or SQLite, and compresses revision history to achieve very high storage efficiency. Security is maintained through regular updates, with SQL injection and cross-site scripting protections built into core output functions.
Originally developed by Magnus Manske and later extended by Lee Daniel Crocker, it has been coordinated by the Wikimedia Foundation since 2003, with an active global developer community contributing to continuous releases.