I've been working my way through Immanion's small-but-quickly-growing catalog of occult nonfiction, and "Gathering the Magic" is yet another excellent example thereof.
The modern magical community is full-to-exploding with all types of groups ranging from the very informal to the detailed-formal. They last anywhere from one ritual to many years, and work with every possible paradigm.
Unfortunately, forming and maintaining a magical group, be it a Wiccan coven, a modern Golden Dawn temple or a druidic grove, presents a series of unique challenges. This is why the vast majority of groups seldom last more than a few years before something explosive (or implosive) occurs to kill it off.
In this book, Farrell pretty much attacks every type of problem that can occur. An obvious veteran of many magical groups (he doesn't even really need to give credentials; it's obvious in his writing), he has pretty much seen it all and lived to tell the tale. No stone is left unturned once it's landed from being thrown, and this makes "Gathering the Magic" an invaluable guide.
Farrell goes through the entire process of group creation and maintenance, from designing a purpose and a group egregore to deciding who the best candidates are (and why discrimination based on race, sex, sexulity, etc are all really stupid ideas) and even how to gracefully end a group once its time has come. He has an excellent section on conflict resolution and also stresses the extreme importance of how groups are meant to train individuals, not sag into mindless masses of followers.
His writing style is superb, and his sense of humor had me laughing out loud every few pages. What could have been a dry, boring text is instead a highly enjoyable journey into his experiences and advice. The anecdotes are well-placed and not overdone. The footnote "It was supposed to be a vulture" had me howling, and you've got to read the book to find out why.
It's also apparent that he's very much in touch with the magical community today. While he acknowledges the good and bad points of group structures that were created in the 19th and 20th centuries, his directions take into account the way the community is in this day and age.
Occasionally I disagree with a point he makes, usually things like "There's a reason you do magic this way and not that way," coupled with a disastrous story. But given his background it's not surprising, and it's also a good warning to newbies that magic isn't always a well-oiled machine--sometimes it does backfire if you're not careful.
Overll, this is by far one of the best books I've read overall, and is a definite must-have for anyone even contemplating starting a group or who already has one. In fact, any magical practitioner who has any contact with any others will get something out of this.