This thesis explores the functional dynamic of a theatrical phenomenon which has for a long time been treated as a given, a convention or a device: direct address to the audience. It is frequently mentioned by scholars and critics, but en passant; its matter, though not its manner, is sometimes dealt with at length. Until recently, however, the significance of direct address has received surprisingly little attention. My MPhil thesis unpicked the strategies of The Life and Opinions of Tristram Shandy, Gentleman by Laurence Sterne using rhetoric as its principle analytical tool. It concluded that this apparently chaotic work of narrative fiction reveals the straight lines of its intent when it is seen as organized by the act of communication between Shandy and his readers rather than by the story it might seem to be trying to tell. Teaching at the Guildford School of Acting, combined professional and academic interests and provided a context in which to investigate the effect which direct address might have in the theatre, where it is both more possible and less surprising than in a work like Tristram Shandy. The research represented in this thesis is founded in my professional practice as well as in the literature. Examined through English Renaissance theatre and its secular and sacred roots, direct address reveals itself as not merely incidental or coincidental: it signals a fundamental interest in communication which is intimately bound up with the persuasive enterprise of rhetoric. It founds a relationship between action and audience which enables a rich and varied play and interplay of idea and story, of suppose and reality, involving audience in the act of theatre both as collaborator and as objective. Though the conventions of naturalism erected a fourth wall, rendering the audience voyeurs rather than participants, Meyerhold and Brecht are shown to have stepped backwards to re-member the self-conscious reflexivity which direct address signals, and recent theatre practice is considered for its exploitation of this key element of theatre.