Wikipedia is written collaboratively by largely anonymous Internet volunteers who write without pay. Anyone with Internet access can write and make changes to Wikipedia articles (except in certain cases where editing is restricted to prevent disruption or vandalism). Users can contribute anonymously, under a pseudonym, or with their real identity, if they choose.
The fundamental principles by which Wikipedia operates are the Five pillars. The Wikipedia community has developed many policies and guidelines to improve the encyclopedia; however, it is not a formal requirement to be familiar with them before contributing.
Since its creation in 2001, Wikipedia has grown rapidly into one of the largest reference websites, attracting 400 million unique visitors monthly as of March 2011 according to ComScore. There are more than 82,000 active contributors working on more than 19,000,000 articles in more than 270 languages. As of today, there are 3,872,070 articles in English. Every day, hundreds of thousands of visitors from around the world collectively make tens of thousands of edits and create thousands of new articles to augment the knowledge held by the Wikipedia encyclopedia (see also Wikipedia:Statistics.)
People of all ages, cultures and backgrounds can add or edit article prose, references, images and other media here. What is contributed is more important than the expertise or qualifications of the contributor. What will remain depends upon whether it fits within Wikipedia's policies, including being verifiable against a published reliable source, so excluding editors' opinions and beliefs and unreviewed research, and is free of copyright restrictions and contentious material about living people. Contributions cannot damage Wikipedia because the software allows easy reversal of mistakes and many experienced editors are watching to help and ensure that edits are cumulative improvements. Begin by simply clicking the edit link at the top of any editable page!
Wikipedia is a live collaboration differing from paper-based reference sources in important ways. Unlike printed encyclopedias, Wikipedia is continually created and updated, with articles on historic events appearing within minutes, rather than months or years. Older articles tend to grow more comprehensive and balanced; newer articles may contain misinformation, unencyclopedic content, or vandalism. Awareness of this aids obtaining valid information and avoiding recently added misinformation (see Researching with Wikipedia).