The MUST HAVE book for any Spirit Keeper, Theurge, or even remotely spiritual Garou player (which should mean everyone). Most of the material presented within is invaluable, and easily tweaked to apply to Mages (you can never go wrong with disdain). The book covers traditional treatments of spirits, chiminage the spirit is willing to accept readily (aside from Gnosis), etc. I can guarantee this book is not the be all end-all of Spirit-lore however, and players will always surprise the STs by thinking up spirits that aren't covered elsewhere. Memorize this book however, and you'll always have a template or guideline to go by in such scenarios.