This article is an attempt to clear up the curious hodge-podge of fact and fiction in Voltaire's play Zaïre. From his facile use of famous names and historical events one receives the impression that the play is at least based on facts. But Voltaire tells us in a letter to M. La Roque (1732): “Je n'ai pris dans l'histoire que l'époque de saint Louis; tout le reste est entierèment d'invention.” Is his statement to be believed? The editors of Zaïre have done nothing to help solve this question.