While perhaps a bit over half the book are pieces penned by Crowley, either directly, or under his various esoteric noms de guerre (Master Therion, Baphomet XI°, etc.), it is much more an "O.T.O. Book" than a "Crowley book", and it's confusing that many (such as amazon.com) insist on listing this as "by Crowley" (to their defense, a different edition of this book than the one I have does say, in rather large letters, "Aleister Crowley" on the cover) whereas much of the book is by others, and even of quite recent vintage.
This volume is a late addition (Vol. 3, No. 10) to the over-all work The Equinox ("The Review of Scientific Illuminism") started by Crowley in 1909. For its first few years, new editions came out twice a year, which then had a substantial gap (after Vol 2 went unreleased), and slowed to every five or six years up to Crowley's death in 1947. Since then new editions have come out sporadically, although the court victories for the O.T.O. in 1985 (over a competing organization headed by Marcelo Motta) seem to have spurred a new cycle of publication via Weiser.
As you are probably suspecting (given the non-specifics of the text), this all does not necessarily present itself as an engrossing read. It swings wildly, from such core texts as Crowley's "channeled' Book Of The Law and the O.T.O. Gnostic Mass to detailed reports about the 1985 lawsuits, with stops at theoretical organizational structures for lodges, etc. (from 1919), and an entire section dealing with the films of Kenneth Anger, sprinkled with some random poetry, essays, and a bit of fiction.
I suppose that if one was somewhat interested in the O.T.O. (and there are quite a number of very active O.T.O. members around L.J.), The Equinox, Volume III, Number 10 would be a decent place to start, although there are quite impressive archives of the key materials available on the web (such as at hermetic.com). This does appear to still be in print, so you could likely find it at your local bookstore. Oddly enough, there don't seem to be any used "deals" on this, as Amazon's new/used vendor listings for it come in only slightly less than Amazon's discounted price, so if this sounds like something you'd want to add to your collection, I guess that's the best you're going to get.