|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.
The software treats all page titles as beginning with a capital letter (unless the first character is not a letter). For information on how to display article titles beginning with lower-case letters (as in eBay), or category titles (as in Category:macOS) see WP:Naming conventions (technical restrictions) § Lowercase first letter.
However, when you create a link with the first letter of the link uncapitalized, as in swimming pool, the first letter of the target page is automatically capitalized in the URL by the software, thus going to the article Swimming pool in this example. However, the remainder of the link (after the initial character) is case-sensitive.
Searching using the Go or Search button is, generally speaking, case-insensitive. It is not necessary to create redirects from alternative capitalizations, unless editors are likely to link from the differently capitalized form. For example, National Park should be created as a redirect to National park, but it is unnecessary to create Isle of wight as a redirect to Isle of Wight. Many such redirects do nevertheless exist, and these are harmless; the only indication to the reader is a small message of the form "(redirected from Isle of wight)". You can use a page-views analysis tool to determine whether a significant number of people ever look for the variant you are thinking of creating a redirect for, or what the frequency of one version is versus another.
It is occasionally acceptable to create two articles (on different topics) with titles that differ only in capitalization, such as Duck sauce and Duck Sauce. If this arises, place a hatnote at the top of each page, linking each to a dedicated disambiguation page or to the other article. It is also acceptable to use names that are differentiated in other ways; which approach should be taken may vary from case to case, balancing such considerations as the risk of confusion in using one set of names against the departure from brevity and common usage in using the other.
In general, each word in English titles of books, films, and other works takes an initial capital, except for articles ("a", "an", "the"), the word "to" as part of an infinitive, and prepositions and coordinating conjunctions shorter than five letters (e.g., "on", "from", "and", "with"), unless they begin or end a title or subtitle. Examples: A New Kind of Science, Ghost in the Shell, To Be or Not to Be, The World We Live In.
English common names of species and of general types of organisms are not capitalized, and article titles about them are sentence-cased, except where proper names appear and are capitalized: Bottlenose dolphin, Livestock guardian dog, Red oak, but Small Indian civet. Redirects should be created from the alternative capitalized form(s), e.g., Bottlenose Dolphin, and from plural forms of each spelling.
For French, see for instance WP:Manual of Style/France and French-related § Works of art. In French, the capitalization rules (for books, works of art, and many other topics) are different from those in English. The situation is further complicated by loanwords, for example a French expression can be adopted in English (such that you'll find it in English dictionaries), but with a different capitalization:
For expressions borrowed from other languages a two-step approach is advised (example explained for expressions borrowed from French):
For Spanish, German, and any language usually written in the Latin alphabet the same (or something similar) would apply.
If the article is about a creative or academic work (such as a book or other written work, movie, album, song, or composition) with a title in a foreign language, or by a non-English-speaking creator, retain the style of the original for modern works. For historical works, follow the dominant usage in modern, English-language, reliable sources.