The Cauldron: A Pagan Forum

...specifically a book on the history and theology of Wicca; with an especial focus on British Traditional Wicca. What does TC suggest?

 
For history: a combination of three books:

• Ronald Hutton's Triumph of the Moon
  
• Philip Heseleton's Wiccan Roots: Gerald Gardner and the Modern Witchcraft Revival (his other works, also good)
  
• Chas Clifton's Her Hidden Children
  

Quite possibly also Philip Heselton's Doreen Valiente: Witch. I've read the other three, but not this one, yet. I also found Mary K. Greer's Women of the Golden Dawn extremely useful in getting the esoteric order influences on the development of Wicca to make any kind of sense (despite being a pretty massive tome, it's also very readable if you like biography at all.)

You want the first three books because they deal with different parts of the history: Hutton is basically up through Gardner, Wiccan Roots deals with a different take on some of the Gardner research and is useful for recalibration and an awareness of what data might or might not exist (and Heselton is a thoughtful historian, but not a formal academic, so he considers different things more or less viable than Hutton does.) Clifton covers the American developments.

Margot Adler's Drawing Down the Moon is an interesting counterpoint to Clifton, since it shows some of the other influences on American Pagan practice in the 70s and into the 80s in particular, but most of her focus is not Wiccan.

In terms of theology, that's a lot more complicated, since British Traditional Wicca rituals are oathbound, and it's sort of hard to talk about the theology given that.

Various groups have exoteric versions of their materials, and there are some larger scale developments (such as the Pagan Way material) but these shouldn't be taken as equivalent in terms of theology, practice, etc. to oathbound material.

Likewise, since Wicca (including BTW) is focused on shared practice rather than shared belief, talking about theology is complicated because it's quite common to have half a dozen people in circle with half a dozen (or a dozen!) different beliefs about any topic, and their personal theologies may vary, even while they agree to do the same practices in the same way when they're together.

For more general Wiccan-influenced but public materials, I think I'd suggest Ivo Dominguez's Spirit Talk (for discussion of deities and other non-physical beings: note that the tradition Ivo works in works with a wide variety of deities rather than BTW's pair of specific deities with oathbound names, so by definition, the theology comes out a bit differently).

For general materials, I really like Thea Sabin's Wicca for Beginners for giving a sense of how bits of practice fit with things.

Reading publicly accessible materials, seeing what people agree on, and doing a bit of contemplating between the lines is the time honoured way to figure out if it's worth finding people to actually talk to in person about it. The Amber and Jet mailing list on Yahoo has a massive archives with tens of thousands of posts: reading through the more active years of those files can be quite informative about general arcs and outlines.