For those of you interested in Tantra, Thelema, Kareeza and other practices using sexual union as a portal, I recommend this highly. It is relatively short but very insightful study of western sexual mysticism from antiquity to contemporary time. Despite the necessary scholarship, it is an easy read.
Versluis provides the reader with a clear understanding of the continuing tradition of sexual mysticism that is seen in Eleusinian mysteries through Gnostics, early Christianity, Cathars, Courtly Love, Alchemy and Qabalah, and other more recent movements. He finishes with a short, but brilliant chapter on the state of sexual mysticism today including the impact of Eastern thought on Western traditions.
Having the background Verslus reveals is helpful to every western aspirant - whether their orientation is tantric or some more western form. He points out that in all of these " . . .what matters is vertical or transcendent union, that is, union of the two individuals not as individuals, but as transcendent beings." The work is especially helpful in sorting out the currents of our common "Christian" heritage (unavoidable if you were raised in the West), demonstrating a much greater diversity and the constant emergence of sexual mysticism not only in movements but also mystics like Jacob Boehme and John Pordage and, poets like Blake, H. D. and T. S. Eliot.
Versluis states "Sexual union becomes sexual mysticism not when two individuals join, but when each lover becomes for the other an opening into the transcendence of I and Thou, an entry into a new new dimension beyond selfhood. In this new dimension, one encounters not only another individuality but the power behind and beyond nature, the principles that inherent in the cosmos."
I am quite certain he has a body of practice. Like any academic, he doesn't talk about his own practice but I do not believe he could not have the insights he does without it. He certainly has facility with Gnosticism and Alchemy. I have always valued good scholarship and have found it beneficial to aiding to my understanding. I feel that practitioners and academics need to co-exist and support each other. The 'shadow' each has upon the other is unfortunate. No one studies in-depth like Versluis without having very strong passion for higher knowledge, beyond the rational mind.