The Psychology of Hashish is an autobiographical essay of Aleister Crowley's experimentation with cannabis. Heavy use of hashish during Thelema rituals comprise the important part of Crowley's philosophy. In this essay, Crowley explains the importance of drug use during the rituals, calling it an aid to mysticism.

Aleister Crowley (1875 – 1947) was an English occultist, ceremonial magician, poet, painter, novelist, and mountaineer. He founded the religion of Thelema, identifying himself as the prophet entrusted with guiding humanity into the Æon of Horus in the early 20th century.