This is a chapter about change: the complex and largely irrecoverable process whereby Athenian tragedy transformed itself into an international art-form which became familiar and influential throughout the Greek-speaking world, was translated and imitated by Roman playwrights, mutated into various types of balletic and operatic performance, and as a select corpus of classical texts helped to shape the educational system, and inform the culture, of later antiquity. The small group of plays that survived into the Byzantine period and beyond have of course had a continuing history of reception, which in recent times has once more become a history of performance (see Chs. 10-12 below). But even for the history of tragedy in the ancient world, the range of space and time covered is too vast, the evidence too diverse and uneven, and the phenomenon itself too elusive for a comprehensive account of this momentous process to be written. As one element in what became an elaborate entertainment industry, tragedy cannot easily be studied in isolation from other dramatic media: in terms of performance and organisation it needs to be considered alongside comedy and (increasingly) alongside musical performance and pantomime. And since the language and iconography of theatre in general invaded the life of later antiquity in innumerable ways, its deeper cultural influence is to be found almost anywhere one cares to look.