This chapter proposes a Role and Reference Grammar (RRG) analysis of externally and internally headed relative clauses, free relatives, non-restrictive relatives, and it-cleft sentences. Particular emphasis is placed on the interface properties of these constructions and the challenges that they pose in the syntax–semantics and semantics–syntax linking. The chapter also reflects on the similarities and differences between relatives and clefts.

Relative clause constructions express an event that functions as a modifier of a referent. As such, relative clause constructions share a participant with the matrix clause -- namely, the referent that they modify. Like other complex sentence constructions, relative clause constructions may be balanced or deranked. The primary differences in strategy involve the expression of the shared participant. The most common strategy is the externally headed strategy: the referent is expressed as a common noun phrase in the matrix clause, and in reduced or zero form in the relative clause. A small minority of languages use strategies that appear to form a continuum from internally headed to correlative to adjoined constructions. Events that function to modify a referent that is a very peripheral participant in the relative clause events form noun-modifying clause constructions; these constructions sometimes use a relative clause strategy. Relative clause construction strategies also systematically vary with respect to the semantic role of the referents in the relative clause event, which are ranked by the Accessibility Hierarchy. Relative clauses may have an anaphoric or indefinite head.