This guideline documents an English Wikipedia naming convention. Editors should generally follow it, though exceptions may apply. Substantive edits to this page should reflect consensus. When in doubt, discuss first on the talk page.

When naming a category, one should be particularly careful and choose its name accurately. Moving non-conventionally categorized pages to another category name (see {{Category redirect}}) imposes an additional overhead – an edit for each article and subcategory. Also, try to avoid names that are too long or too short. Short, straight-forward names, are preferred for categories, though it may be necessary at times to deviate from this principle for clarity or disambiguation.

General conventions

• Names of topic categories should be singular, normally corresponding to the name of a Wikipedia article. Examples: "Law", "France", "Hillary Clinton".
• Names of set categories should be plural. Examples: "Writers", "Villages in Poland".
• Note that in many instances a topic category and a set category have similar names, the topic category being singular and the set category plural. For example, Opera is a topic category (containing all articles relating to the topic), while Operas is a set category (containing articles about specific operas). Be careful to choose the right one when categorizing articles.
• Do not write the category structure in names. Example: "Monarchs", not "People – Monarchs". This includes creating categories that are subpages of other categories.
• Choose category names that can stand alone, independent of the way a category is connected to other categories. Example: "Geography terminology stubs", not "Terminology" (a subcategory of "Geography stubs").

Categories for articles

• Standard article naming conventions apply; in particular, use sentence case, do not use title case. Specifically, do not capitalize regular nouns except when they come at the beginning of the category name.
• When naming, use words and phrases which exist in verifiable reliable sources (particularly for technical subjects), so that those sources may be used to support inclusion of information.
• Avoid abbreviations. Example: "Category:Military equipment of World War II", not "Category:Military equipment of WW2". However, acronyms that have become the official, or generally used, name (such as NATO) should be used where there are no other conflicts. Exceptions to this should be explained in the category description.
• Avoid subjective adjectives such as famous, large, or beautiful in category titles.
• When a topic requires disambiguation, any category eponymously named for that topic should include the same form of disambiguation, even if no other articles are likely to have an eponymous category.
• If there are more than a few lists in a particular subject area, it may be appropriate to create a specific subcategory that contains only the list pages and no other types.
  • As an example Category:Countries contains the subcategory "Category:Lists of countries", which in turn contains the list pages "List of Soviet Republics", and "List of countries by population".
  • When placing list pages in such a category, use a sort key to adjust the page title to exclude the starting words "List of", or all lists would appear under "L". For example, when adding List of Soviet Republics to the category, using Category:Lists of countries|Soviet Republics and will make it be sorted in the S section. See also Category:Lists.
• Naming guidelines for sub-categories of Category:Stub categories are listed at Wikipedia:WikiProject Stub sorting/Naming guidelines § Categories.

Project categories

• Categories used for Wikipedia administration, are disambiguated by prepending with the word "Wikipedia" (no colon) if this is needed to prevent confusion with content categories. For example, Category:Inactive project pages (where no confusion is likely), but Category:Wikipedia tools (as distinct from the content category Tools).
• All WikiProject categories should have "WikiProject" (or "WikiProjects") as part of the name. Note that this does not apply to the names of categories that projects might create for the use of assessments. In these cases, the advice given in Project Categories, which conforms to Category:Wikipedia 1.0 assessments is advised, though not mandatory.
• For geographical photo requests, the category name should be "Wikipedia requested photographs in xxx" as in Category:Wikipedia requested photographs in England; see Category:Wikipedia requested photographs by location.
• For categorization in userspace, see Wikipedia:Categorization § User namespace and Wikipedia:User categories § Naming conventions.