This paper explores issues relating to signaling word boundaries from the perspec tive of Aylett's Smooth Signal Redundancy proposal (Aylett 2000, Aylett andTurk 2004) that language has evolved to spread redundancy, i.e. recognition likelihood, evenly throughout utterances. In Aylett's proposal, information that enables lis teners to identify sequences of elements in an utterance (signal redundancy) comes from two sources: a) language redundancy, recognition likelihood based on lex ical, syntactic, semantic, pragmatic and other factors, and b) acoustic redundancy, recognition likelihood based on acoustic salience. Smooth signal redundancy is achieved by a complementary relationship between language redundancy and acoustic redundancy that is implemented via prosodic structure.While Aylett and Turk (2004) present the case for prosodic prominence as a l ever for modulating the acoustic salience of syllables, the current paper proposes that prosodic constituency also fulfils this function for words. The current paper proposes that the signal redundancy, or recognition likelihood, of words can be manipulated by signaling their boundaries, and that the occurrence and strength of these boundary markers correlates inversely with language redundancy. Pro sodic constituency implements the complementary relationship between language redundancy and word boundary salience.Smooth Signal Redundancy provides an integrated explanation for a set of prop erties relating to prosodic constituent structure.