|This page in a nutshell: Readers must be able to check that any of the information within Wikipedia articles is not just made up. This means all material must be attributable to reliable, published sources. Additionally, quotations and any material challenged or likely to be challenged must be supported by inline citations.|
In the English Wikipedia, verifiability means other people using the encyclopedia can check that the information comes from a reliable source. Wikipedia does not publish original research. Its content is determined by previously published information rather than the beliefs or experiences of editors. Even if you are sure something is true, it must be verifiable before you can add it. If reliable sources disagree, then maintain a neutral point of view and present what the various sources say, giving each side its due weight.
All material in Wikipedia mainspace, including everything in articles, lists, and captions, must be verifiable. All quotations, and any material whose verifiability has been challenged or is likely to be challenged, must include an inline citation to a reliable source that directly supports the material. Any material that needs an inline citation but does not have one may be removed. Please immediately remove contentious material about living people that is unsourced or poorly sourced.
For how to write citations, see citing sources. Verifiability, no original research, and neutral point of view are Wikipedia's core content policies. They work together to determine content, so editors should understand the key points of all three. Articles must also comply with the copyright policy.