Aristophanes' comic masterpiece Thesmophoriazusae has long been recognized amongst the plays of Old Comedy for its deconstruction of tragic theatricality. This book reveals that this deconstruction is grounded not simply in Aristophanes' wider engagement with tragic realism. Rather, it demonstrates that from its outset Aristophanes' play draws upon Parmenides' philosophical revelations concerning reality and illusion, employing Eleatic strictures and imagery to philosophize the theatrical situation, criticize Aristophanes' poetic rival Euripides as promulgator of harmful deceptions, expose the dangerous complicity of Athenian theatre audiences in tragic illusion, and articulate political advice to an audience negotiating a period of political turmoil characterized by deception and uncertainty (the months before the oligarchic coup of 411 BC). The book thereby restores Thesmophoriazusae to its proper status as a philosophical comedy and reveals hitherto unrecognized evidence of Aristophanes' political use of Eleatic ideas during the late fifth century BC.