To ensure Wikipedia's integrity and accuracy, all content must be independently verifiable, requiring editors to cite credible third-party sources. A related policy is that editors cannot contribute original research; all information must have been previously published in reputable, editor-reviewed publications.
Determining what counts as a reliable source is a complex and often contested matter. Since Wikipedia editors are not required to prove their personal expertise before editing in any given topic, they defer to the authority of experts and professionals whose professional role incentivizes accuracy.
As a result, reliable sources commonly include academic and peer-reviewed journals, books by reputable publishers, and established news organizations like major newspapers and magazines. While a publication need not be nonpartisan to be considered reliable, those focused on reporting rather than opinion are generally more trusted. In certain cases, government documents and work by recognized subject matter experts may also be used.
Even generally reliable sources may publish some material Wikipedia prefers not to use. For instance, newspaper opinion pieces may lack the fact-checking of staff articles, and some sources may be reliable in certain areas but not others. Many outlets now feature unpaid "contributors" whose writing is not afforded the same credibility as professional journalists. Sensationalist media like tabloids, and self-published sources such as blogs and social media, are generally not considered reliable.
