Wikimedia Commons (or simply Commons) is an online repository of free-use images, sound and other media files. It is a project of the Wikimedia Foundation, from which uploaded files can be used across all Wikimedia projects in all languages, including Wikipedia, Wikibooks, Wikisource and Wikinews, or downloaded for offsite use. The repository contains over seven million media files.
The project was proposed by Erik Möller in March 2004 and launched on September 7, 2004. A key motivation behind the setup of a central repository was the desire to reduce duplication of effort across the Wikimedia projects and languages, as the same file had to be uploaded to many different wikis separately before Commons was created.
Given its primary function as a supporting project for the other Wikimedia web sites, the main content policy for files uploaded to Commons is that they must be potentially useful on any of the Wikimedia projects. This excludes material such as purely personal pictures and artwork, in contrast to image sharing repositories like Flickr, Photobucket and DeviantArt. Nevertheless, large numbers of files hosted on Commons are not used directly on any Wikimedia project and likely never will be; as such, the project has grown into a repository of multimedia in its own right, which is frequently linked to from articles on Wikipedia and other Wikimedia websites to provide supplemental materials.
Most Wikimedia projects still allow local uploads which are not visible to other projects or languages, but this option is meant to be used primarily for material which local project policies allow, but which would not be permitted according to the copyright policy of Commons, such as fair use content. Wikimedia Commons itself does not allow fair use or uploads under non-free licenses, including licenses which restrict commercial use of materials or disallow derivative works. Licenses that are acceptable include the GNU Free Documentation License, Creative Commons Attribution and Attribution/ShareAlike licenses, other free content and free software licenses, and the public domain.
The default language for Commons is English, but registered users can customize their interface to use any other available user interface translations. Many content pages, in particular policy pages and portals, have also been translated into various languages. Files on Wikimedia Commons are categorized using MediaWiki's category system. In addition, they are often collected on individual topical gallery pages. While the project was originally proposed to also contain free text files, these continue to be hosted on a sister project, Wikisource.