Master’s Thesis for the Western Esotericism programme at the University of Amsterdam which investigates the role of peyote in the Magick of Aleister Crowley and in the development of Thelema. The content of this thesis supersedes the content of 'Aleister Crowley's magical use of Anhalonium Lewinii' a.k.a. 'The complexities of Aleister Crowley’s magical relationship with anhalonium lewinii'.