Keith Thomas' celebrated theory of the decline of magic during the seventeenth century, and its disappearance by the twentieth century, stands in stark contrast to the magia naturalis of the Renaissance and the later occult revival of the fin de siecle from which Wicca developed. In this thesis we contend that in the ferment of Renaissance Europe, magic remained an integral part of western esotericism, of which Wicca in the 1990s is a current manifestation. Using Antoine Faivre's characterisation of esotericism and Wouter Hanegraaffs historical emphasis on esoteric connections, we construct a framework to enable us to assess Wicca as an esoteric religious tradition in the 1990s. Within this framework, and running throughout the thesis, we investigate an apparent transformation in the understanding and practice of magic. We argue not only that Wicca is a specific religion and part of the Western Esoteric Tradition, but that the use and understanding of magic in Wicca is not divorced from, but part of religion; rather than a contra-religious, instrumental means of control utilised by individuals, magic may thus instead be understood as a participative group religious practice. This thesis thus seeks to go beyond the conflation of Wicca with other forms of witchcraft and paganism in order to uncover Wicca as a specific form of spiritual expression. The seemingly ever-increasing popularity of Wicca in the Protestant world suggests that Thomas' theory, whilst accurate for the restricted historical epoch with which he engages, in fact requires revision as a consequence of the development of Wicca as a religion in the second half of the twentieth century. Thus, instead of religious changes causing a decline in magic, as we approach the twenty-first century it may in fact be more appropriate to speak of religion and the return of magic.