This thesis seeks to establish how the fifth-century audience’s perception of Aeschylean tragedy was influenced by their prior knowledge of the myths on which the dramas were based. Thus we study references to these myths in earlier epic and lyric sources in an attempt to detect borrowings and deviations from the earlier material on the part of the poet. The earliest surviving tragedy, the Persae, has a historical basis and so mythical knowledge is supplanted by the audience's own first-hand experience of the recent war. We see how foreknowledge of the Greek victory at Salamis will prove a deep influence on the audience s perception of the presentation of the enemy court and how Aeschylus presents the Persians as being utterly devastated by the defeat. Likewise an appreciation of the Seven Against Thebes is greatly enhanced if we remember that from the very beginning of the drama the audience were anticipating the double fratricide from their knowledge of this events in previous versions of the myth. During the Supplices, the audience would have suspected that not only would the Argives accept the supplication of the Danaids but also that these helpless girls would shortly murder their bridegrooms on their wedding-night, and Aeschylus includes many dark hints at this future event during the course of his play. Our study of the myth of Agamemnon will enable us to appreciate the exploitation of audience expectation throughout the Oresteia and their foreknowledge that murder is plotted against Agamemnon on his return and that Orestes will return to exact vengeance proves vital to the tragic effect. In addition we detect certain areas in which Aeschylus may diverge from his inherited material, such as his presentation of Clytemnestra as the sole unaided killer of her husband and his inclusion of a trial of Orestes before the court of the Areopagus. Thus it is hoped that by considering the mythical knowledge shared by both Aeschylus and his audience we are able to gain a fuller appreciation of the effects sought by the poet in the fifth-century theatre.