Wikipedia is a free online encyclopedia that anyone can edit, and millions already have.

Wikipedia's purpose is to present information on all branches of knowledge. It consists of freely editable content, with articles that contain numerous links guiding readers to more information. Wikipedia is one of many Wikimedia projects hosted by the nonprofit Wikimedia Foundation.

Wikipedia is written by human volunteers known as Wikipedians who collaborate with almost no assistance from artificial intelligence. Wikipedia articles can be edited by anyone with Internet access, except in limited cases in which editing is restricted to prevent disruption or vandalism. Since its creation on January 15, 2001, it has grown into the world's largest reference website, attracting over a billion visitors each month. Wikipedia is a multilingual project, with more than sixty-seven million articles in more than 300 separate wikis for almost as many languages. This includes 7,183,588 articles in English, with 275,751 active contributors in the past month.

Wikipedia's fundamental principles are summarized in its five pillars. While the Wikipedia community has developed many policies and guidelines, new editors do not need to be familiar with them before they start contributing.

The quality of content is more important than the expertise of who contributes it. Wikipedia's content must conform with its policies, including being verifiable by published reliable sources. Contributions based on personal opinions, beliefs, or personal experiences, unreviewed research, libellous material, and copyright violations are not allowed and will not remain. Wikipedia's software makes it easy to reverse errors, and experienced editors watch and patrol bad edits.

Wikipedia differs from printed references in important ways. Anyone can instantly improve it, add quality information, remove misinformation, and fix errors and vandalism. Since Wikipedia is continually updated, encyclopedic articles on major news events appear within minutes.

For over 25 years, Wikipedians have volunteered their time and talents to create history's most comprehensive encyclopedia while providing references and other resources to researchers worldwide (see Researching with Wikipedia). In summary, since 2001 Wikipedia has tested the wisdom of the crowd and has found that it succeeds.

To start editing, simply click the Edit or Edit source button, or the pencil icon , at the top of any non-protected Wikipedia page or section.