An indefinite pronoun is a pronoun which does not have a specific, familiar referent. Indefinite pronouns are in contrast to definite pronouns.

Indefinite pronouns can represent either count nouns or noncount nouns. They often have related forms across these categories: universal (such as everyone, everything), assertive existential (such as somebody, something), elective existential (such as anyone, anything), and negative (such as nobody, nothing).

Many languages distinguish forms of indefinites used in affirmative contexts from those used in non-affirmative contexts. For instance, English "something" can be used only in affirmative contexts while "anything" is used otherwise.

Indefinite pronouns are associated with indefinite determiners of a similar or identical form (such as every, any, all, some). A pronoun can be thought of as replacing a noun phrase, while a determiner introduces a noun phrase and precedes any adjectives that modify the noun. Thus, all is an indefinite determiner in "all good boys deserve favour" but a pronoun in "all are happy".

Most indefinite pronouns correspond to discretely singular or plural usage. However, some of them can entail singularity in one context and plurality in another. Pronouns that commonly connote indefiniteness are indicated below, with examples as singular, plural, or singular/plural usage.

English has the following quantifier pronouns:

Some of the English indefinite pronouns above have possessive forms. These are made as for nouns, by adding 's or just an apostrophe following a plural -s (see English possessive).

The most commonly encountered possessive forms of the above pronouns are: