Established in 2001, Wikipedia is an free-access digital encyclopedia written in a variety of languages by volunteers around the world, whose articles can be edited by anyone. It uses wiki technology, which facilitates content editing and storage of the page’s history of changes. Founded by American entrepreneur Jimmy Wales, with the help of philosopher Larry Sanger, it has been overseen by the Wikimedia Foundation since 2003.

Wikipedia started on 15th January 2001 as a complementary project for Nupedia, an encyclopedia written by experts whose articles were peer-reviewed. The latter was designed to create articles of a quality comparable to that of professional encyclopedias thanks to the participation of scholars, mainly PhD students and academics, who were asked to contribute on a volunteer basis. Due to the slow progress made on the project, a wiki linked to Nupedia was created in 2001, initially intended to expedite the creation of articles in parallel before undergoing the peer-review process. Both projects coexisted until the success of Wikipedia ended up eclipsing Nupedia, which ceased operations in 2003. Figuring among the ten most visited websites in the world, the encyclopedia has continuously grown. It currently offers more than 35 million articles in 288 languages, including some indigenous languages, other invented ones, like Esperanto, and even dead languages, like Latin. Twelve of its language editions surpass one million articles (English, Dutch, German, French, Italian, Polish, Spanish, Russian, Swedish, Vietnamese, Cebuano and Waray-Waray, both spoken in the Philippines) and three others have more than 700,000 (Chinese, Japanese and Portuguese). English Wikipedia is the most extensive, with over 4,800,000 articles. Wikipedia currently has more than 25 million registered users, about 73,000 of whom are active editors, and receives about 500 million single visits a month.

Created in 2003 with headquarters in San Francisco (USA), the Wikimedia Foundation controls and manages Wikipedia. It also has other projects that complement the encyclopedia, all of which are multilingual, open and supported by wiki technology: Wiktionary, aimed at creating an open dictionary; Wikibooks, which makes open-content textbooks, manuals and instructional guides available for free to any Internet user; Wikiversity, a free and open online education platform allowing the creation of learning projects at all levels of education or the development of didactic material such as examinations and practical exercises; Wikiquote, a compendium of quotations and sayings in every language, which also includes their sources; Wikinews, an open-content news source; Wikisource, an online library of original texts that have been published under a free licence or in the public domain; Wikimedia Commons, a database of images and multimedia material for other projects; Wikispecies, a free and open directory of biological species; Meta-Wiki, a website to support other Foundation projects; Wikidata, a database; and Wikitravel, a travel guide.