What types of sources count as reliable on Wikipedia?

The reliable-source definition is operationally specific and the answer to which sources qualify is fairly mechanical once the standard is understood. The strongest sources are major newspapers with established editorial standards (the Wall Street Journal, the Financial Times, Bloomberg, Reuters, the New York Times, the Washington Post, the Associated Press, and equivalents internationally). Academic journals and peer-reviewed articles are strong sources for any claim in their field. Books from established publishers with editorial processes are reliable. Authoritative reference works (the Encyclopedia Britannica for general subjects, specialist encyclopedias and handbooks for their fields) are reliable. Trade publications with professional editorial standards qualify on a case-by-case basis. The distinction is most actionable at the readiness stage, when we evaluate whether the existing coverage can support an article.