Capitalization

Capitalization is the system of using capital letters at particular places in written text. It helps indicate sentence boundaries, identify proper nouns, and convey emphasis or formal style. Capitalization rules vary by language and style guide, and they can affect meaning or readability if misapplied.

In English, capitalization commonly follows several core rules: the first letter of a sentence is capitalized; proper nouns such as personal names (Alice), geographic places (Paris), organizations (World Health Organization), and languages (English) are capitalized; the pronoun I is always capitalized; days of the week, months, nationalities, and ancestral terms (British, Japanese) are capitalized; acronyms and initialisms (NASA, UNESCO) are capitalized; titles of works are capitalized to varying extents depending on style (see below).

In titles and headings, capitalization commonly uses title case—major words capitalized while short articles, conjunctions, and prepositions are lowercased except when they occur as the first or last word. Some style guides differ on which words count as major; others use sentence case in which only the first word and proper nouns are capitalized.

Capitalization conventions also vary by language. For example, German capitalizes all nouns, while French and Spanish generally do not capitalize common nouns or after colon in some contexts. Historical usage has shifted, with English texts modernizing or broadening norms over time to favor fewer capitalized words outside proper nouns.