by Gershom Scholem.
This is one of my favorite books. It is very authoritative, descriptive, easy to unertsand and provided me with great insight. All of Gershom Scholem's books are recommended.
Note from Amazon: Gershom Scholem, who died in 1982, remains the biggest gun in kabbalah scholarship, and On the Kabbalah and its Symbolism is perhaps his most accessible book on the subject. It contains definitive essays on the relation of the Torah to Jewish mysticism, the mythology of the kabbalah, and the place of Jewish mystics in the Jewish community. This book helped reinvigorate 20th-century Jewish studies with an awareness of the living reality of God, after the 19th century's more astringent scholarly emphasis on law and philosophy. It shows how Jewish mystics have been less concerned with adherence to orthodoxy than their Christian counterparts, and freer in their expression of the divine aspects of eroticism. Furthermore, Scholem offers great insight regarding the ways that kabbalah has not only threatened the authority of institutional religion, but also served as a source of its vitality. --Michael Joseph Gross. Paperback: 240 pages. Publisher: Schocken (January 30, 1996).
Other excellent books on Kabbalah by Gershom Scholem:
Origins of the Kabbalah 504 pages. January 1, 1991.
Major Trends in Jewish Mysticism 460 pages. 1969.