Based on a series of lectures that Rabbi Aryeh Kaplan gave to a small group of students in Brooklyn in 1981, this contains transcripts of the series on the kabbalistic system, and testifies to his wonderful ability to transmit profound ideas in a readily-graspable way. Although this is an introductory text, it contains many perspectives that are expressed in a unique way, so it would be quite valuable even for the more advanced student of Jewish mysticism.