Kabbalah (literally “the receiving” [of tradition]) is an early form of Jewish mysticism. Key concepts include the ten sefirot (heavenly spheres), the Hebrew alphabet, Shiur Qomah (dimensions of the divine body), the archangel Metatron, and the Shekhinah (the feminine aspect of the Godhead). The main books of the Kabbalah, written in early antiquity, include Sefer Yetzirah (Book of Creation), an early and major source, thought to be from the 3rd century ce, whose commentaries constitute most subsequent Kabbalistic literature and Sefer ha’Bahir (Book of Enlightenment), first published in the early 12th century. Both works discuss the ten sefirot and the Hebrew letters. Other works are the Hekhalot (Palace) literature, which includes the ritual praxis of “descending to the Chariot” and hymns recited in a celestial Temple, the Apocalypse of Abraham, the book of Enoch, and sections of the Dead Sea scrolls. In the Mishnah Hagigah (220 ce), two variants of Kabbalah are mentioned: the study of Creation and the study of the Heavenly Chariot. These two categories are linked to biblical prooftexts: the study of creation to the first chapter of Genesis, and the study of the Heavenly Chariot to the first chapter of the book of Prophet Ezekiel. Of the Kabbalistic treatises and texts written in the medieval period, the most important ones are the book of the Zohar (Splendor) by Moses de Leon (c. 1240–1305) and possibly other authors, and the writings of Abraham Abulafia (1240–c. 1291) and that of his student Joseph Gikatilla. The book of the Zohar is distinguished by a reliance on the ten sefirot, although couched in esoteric references, while the many books by Abulafia present linguistic mysticism with permutations of divine names. The former emphasis on the sefirot is also known from the ‘Iyyun (Study) Group in Provence, and Azriel of Gerona (1160–1238), whereas in works by the Hasidei Ashkenaz (German Pietists), led by Judah the Pious (1150–1217) and Eleazar of Worms (c. 1176–1238), numerology and angelology are basic tools.