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

Wikipedia's purpose is to benefit readers by presenting information on all branches of knowledge. Hosted by the Wikimedia Foundation, Wikipedia consists of freely editable content, with articles that often contain numerous links guiding readers to more information.

Written collaboratively by largely anonymous volunteers known as Wikipedians, 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 currently has more than sixty-three million articles in more than 300 languages, including 6,912,670 articles in English, with 121,641 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.

Anyone can edit Wikipedia's text, references, and images. The quality of content is more important than who contributes it. The content must conform with Wikipedia's policies, including being verifiable by published reliable sources. Contributions based on personal opinions, beliefs, personal experiences, unreviewed research, libellous material, and copyright violations are not allowed and will not remain. Wikipedia's software allows easy reversal of errors, and experienced editors watch and patrol bad edits.

Wikipedia differs from printed references in important ways. It is continually created and updated, and encyclopedic articles on news events appear within minutes, making it more dynamic than most traditional resources. Anyone can improve Wikipedia, and more than 23 years of volunteer editors giving their time and talents to the project have made Wikipedia history's most comprehensive encyclopedia. Its editors add quality and quantity, remove misinformation, and fix errors and vandalism. The sources they provide are used by researchers worldwide (see Researching with Wikipedia).

In summary, Wikipedia has tested the wisdom of the crowd since 2001 and has found that it succeeds.

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