The Jewish metaphysical system of the Holy Kabbalah posits a vertical and positively-aligned Tree of Life, through which energy from the earthly plane flows upward in a series of experiences culminating in union with the Divine Source. However the Kabbalah, as we know it today, was not the only mystical formulation that emerged in the 12th century. Other versions, with different names and attributions of power, were also envisioned. Sefer ha-Sitra Achra: The Book of Descent explores the origins and true meaning of the 'Sitra Achra, the demonic 'Other Side' of Jewish Mysticism. Using historical source documents, it examines an alternative Kabbalah, and the demonic forces with which it is associated. Included among them are Samael and Lilith, Asmodeus and the 'Younger' Lilith. Their relationship with each other, and their influence upon our world, including the 'Garden of Eden' and subsequent expulsion, is also examined. Also included is a detailed description of 'The Ritual of Descent' a powerful and effective scrying exercise designed to enable the seeker to journey to the realms of the other side and to commune with the entities present.