In grammar, a conjunction (abbreviated conj or cnj) is a part of speech that connects two words, sentences, phrases or clauses. A discourse connective is a conjunction joining sentences. This definition may overlap with that of other parts of speech, so what constitutes a "conjunction" must be defined for each language. In general, a conjunction is an invariable grammatical particle, and it may or may not stand between the items it conjoins.

The definition may also be extended to idiomatic phrases that behave as a unit with the same function, for example as well as, provided that.