In the 1950s, the English occultist Gerald Gardner (1884–1964) began propagating a magico-religious tradition now known as Gardnerian Witchcraft whose adherents today number in the hundreds of thousands. A common element of Wiccan belief is an ethical commandment known as the “Wiccan Rede,” usually articulated in the form “an' it harm none, do what ye will.” This article traces the history of the Rede, beginning with an examination of Gardner's own early ethical statements. It traces Gardner's relationship with Doreen Valiente, his collaborator who came to proclaim the Rede at a prominent Pagan gathering in October 1964, noting the influence of Crowley's law of thelema, before moving on to discuss the wider reception of the Rede within the Wiccan movement and why practitioners of many rival traditions chose to reject it.