The most notoriously transgressive figure in modern Western esotericism is Aleister Crowley, and his best-known precept is “Do what thou wilt”. This precept arrived in Crowley's work with deeply subversive overtones, from sexual excess (Pierre Louÿs) to proto-fascism (Nietzsche), although its roots lie in the mainstream of Western culture (Augustine, Rabelais). This paper will show how the precept was domesticated in the course of the twentieth-century, largely through its adoption by Gerald Gardner and the Wiccan movement as part of the “Wiccan Rede”: “An it harm none, do what ye will”. The precept has evolved into an unthreatening truism: an essentially uncontroversial statement of classical liberal ethics (corresponding to J.S. Mill's “harm principle”). This in turn reflects the mainstreaming that esoteric religion experienced in the twentieth-century, as it moved from the Crowleyan periphery to something approaching suburban respectability.