From The Art and Popular Culture Encyclopedia
Within the modern system of Thelema, developed by occultist Aleister Crowley in the first half of the 20th century, Thelemic mysticism is a complex mystical path designed to do two interrelated things: to learn one's unique True Will and to achieve union with the All. The set of techniques for doing so falls under Crowley's term Magick, which draws upon various existing disciplines and mystical models, including Yoga, Western ceremonial ritual (especially invocations and eucharistic ceremony), the Qabalah, and several divination systems, especially the tarot and astrology.
The path to mystical attainment or enlightenment was initially developed by Crowley largely based on the meditation/mystical techniques found in Buddhism and also the Tree of Life, especially as it was examined by Eliphas Levi in the 19th century and later by various members in the occult society, the Golden Dawn. In 1904, Crowley claimed to have transcribed, via "direct-voice transmission" from a "praeternatural intelligence" named Aiwass, The Book of the Law, which he eventually called the central sacred text of Thelema, heralding a new Aeon for mankind.
Between 1907 and 1911, Crowley wrote a series of other small texts which he considered to be "inspired" in that they were written through him rather than by him, which were afterwards collected together and termed the Holy Books. The final text added to the list was The Vision and the Voice, a vivid account of Crowley's astral travels through the thirty Enochian Aethyrs. These texts formed the final mystical backbone of Crowley's system.