Capitalization is the writing of a word with its first letter in uppercase and the remaining letters in lowercase.

Capitalization custom varies with language. In Latin and ancient Greek, only proper nouns are capitalized. In most modern languages, the first word in a sentence is capitalized as well. In the English language the word I is always capitalized, and many authors capitalize all words in a title except conjunctions and articles.

Many other languages, such as German, capitalize all nouns.

Some other miscellaneous rules:

  1. In English, in addition to proper nouns, proper adjectives (those derived from a name, such as Canadian, Shakespearian) are written with initial majuscules, as are the names of days of the week, months, languages, and the pronoun I.
  2. In German, all nouns are written with an initial majuscule.
  3. In Dutch, if a proper noun starts with the diphthong ij both i and j are capitalized. Examples: IJmuiden and IJssel. This because ij is not really two letters, but is actually a ligature ij/IJ.
  4. Also in Dutch, 't, d', or 's in names or sayings are never capitalized, as they are short for the articles het and de (or the old possessive form des). Examples: 's Gravenhage (from des Graven Hage), d'Eendracht (from de Eendracht), 't Theehuis (from het Theehuis).
  5. In the Danish or Norwegian languages, Æ/æ is a single letter, and both 'a' and 'e' must be capitalized.
  6. In Romance languages, days of the week, months, and adjectives are not written with initial majuscules.
  7. In Spanish, the abbreviation of the pronoun usted, Ud. or Vd., is usually written with a capital. The same goes for the Italian pronoun Lei, the German Sie, and the Dutch U, when these are used as a respectful second-person pronoun (see T-V distinction).
  8. Some Romance languages capitalize specific nouns; for example, French often capitalizes such nouns as l'État (the state) and l'Église (the church) when not referring to specific ones.
  9. Many European languages capitalize pronouns used to refer to God or a god.

The full rules of capitalization for English are complicated and have changed over time, generally to capitalize fewer terms; to the modern reader, an 18th century document seems to use initial capitals excessively. It is an important function of English style guides to describe the complete current rules.

For some terms a capital as first letter is avoided by avoiding their use at the beginning of a sentence, or by writing it in lowercase even at the beginning of a sentence. E.g., pH looks unfamiliar written "PH", and m and M may even have a different meaning, milli and mega. Brands are sometimes chosen to start with a lowercase letter, to be special, e.g. easyJet. A related oddity is including a punctuation mark in a brand name, e.g. "Yahoo".

Some individuals choose not to use capitals with their names, such as k.d. lang. E. E. Cummings, whose name is often spelt without capitals, did not spell his name so; the usage derives from the typography used on the cover of one of his books.

See also: Bicapitalization