|This guideline documents an English Wikipedia naming convention.|
|This page in a nutshell: Article titles should be in sentence case, not title case. Only the first word is capitalized, except for proper names.|
Do not capitalize the second or subsequent words in an article title, unless the title is a proper name. For multiword page titles, one should leave the second and subsequent words in lowercase unless the title phrase is a proper name that would always occur capitalized, even mid-sentence.
This convention often also applies within the article body, as there is usually no good reason to use capitals. Outside Wikipedia, and within certain specific fields (such as medicine), the usage of all-capital terms may be a proper way to feature new or important items. However these cases are typically examples of buzzwords, which by capitalization are (improperly) given special emphasis.
For details on when to capitalize on Wikipedia, see the manual of style sections on capital letters and, when relevant, on trademarks. When in doubt, reliable reference works for capitalization conventions and other style matters may be useful. Note that all style guides conflict on some points; the Wikipedia MoS and naming conventions are a consensus-based balance between them, drawing primarily upon academic style, not journalistic or marketing/business styles, and taking into account Wikipedia-specific concerns.