The goal of this article is to uncover the system underlying three types of English relative clauses, and to characterise their distinctive uses in discourse: NP-integrated ones, namely restrictive and ‘a-restrictive’ relative clauses, and non-integrated ones, represented by non-restrictive relatives.The area at issue is central, since understanding the functioning of these constructions requires reference to the fundamental interface between grammar (language system) and discourse (language use). The discourse functions of the three subtypes of relatives are claimed to be underlain by their intrinsic morphosyntactic and semantic properties. A major aim is to highlight the relative degree of ‘communicative dynamism’ of each subtype of relative clause, in terms of its respective contribution to the construction of discourse.In doing so, the article focuses on the distinctive properties of presupposed as well as non-presupposed restrictive relatives, and of definite as well as indefinite NPs containing integrated relatives more generally. Along the way, it critically examines certain controversial conceptions of the structural and functional features of the constructions at issue, and, in particular, the claim that there is no essential distinction to be drawn between ‘integrated’ and phrase-external relative clause subtypes at all.