Few words have maintained such a hold over both theatrical practice and classical philology as Aristotle's term katharsis in his Poetics. This chapter explores some aspects of the cultural background to his brief, compressed and elliptical discussion of katharsis as an objective of tragic theatre. It argues that Aristotelian tragic katharsis, although clearly signalling a useful transformation through an aesthetic experience, must remain enigmatic since the noun had many different metaphorical resonances. Aristotelian katharsis is the counterpart, in the realm of ideology, to massive changes occurring on the political and cultural levels of the ancient Mediterranean and Black Sea worlds at the very transition between 'classical' and 'Hellenistic' society. Aristotle's theory of katharsis—whatever the procedure metaphorically underlying it—is a component, probably an important one, of his defence of tragic theatre. The context in which Aristotle's enigmatic statement needs placing is the evidence of earlier Greek acknowledgement of the transformative effect of tragic theatre.