This is the first official, annotated edition of the complete magical diaries of the Swiss-American occultist Leah Hirsig (1883–1975), lover and disciple of the British occultist Aleister Crowley (1875–1947), self-styled Great Beast 666 and founder and prophet of the new religion Thelema. A schoolteacher by training, who lived, loved, and traveled independently, Hirsig embodied New Woman ideals in her life and in her attraction to a counternormative occult movement. In the early 1920s, Hirsig was appointed Crowley’s Scarlet Woman—a title that identified her as the earthly avatar of the Thelemic goddess Babalon and as Crowley’s feminine counterpart. In this role, Hirsig was essential in stewarding the Thelemic community during an eventful period, which coincided with the establishment of an Abbey of Thelema at Cefalù, Sicily, and the authorship of several of Crowley’s important magical works. In 1924, Hirsig was replaced as Scarlet Woman but remained devoted to Thelema for several years. Hirsig’s magical diaries provide a unique window onto the possibilities and challenges faced by women occultists in the early twentieth century. They highlight how occult movements offered heightened opportunities for women’s leadership but were also impacted by wider gender inequalities. The diaries are presented with a selection of previously unpublished letters and poems by Hirsig and Crowley, which shed further light on their relationship and the period from Hirsig’s attraction to Thelema in 1919 until her departure from the movement in 1927–1930. The book also includes an extensive editorial introduction that situates Hirsig within Thelema, twentieth-century occultism, and women’s changing roles during this period.