The schools of the kabbalists from the late 12th century to now are just one manifestation of esotericism and mysticism in Jewish religious culture. ‘Ancient Jewish Mysticism and the Emergence of the Kabbalah’ considers the beginnings of Jewish esotericism and looks at how and when the Kabbalah appeared in documented form. One of the most important sources for medieval kabbalistic terminology is an ancient non-kabbalistic treatise called Sefer Yezira (The Book of Creation). This is not, as many think, the earliest work of the Kabbalah. It is a cosmological, scientific treatise. The central concept in the work is harmonia mundi (harmony of the universe).