The Elements of Ritual:
Air, Fire, Water & Earth in the Wiccan Circle

Many books may tell you how to cast a Wiccan circle, but none really bother to explain why. When you've finished reading The Elements of Ritual, you'll know what each step of the circle-casting ceremony means, why it's there, and what it accomplishes. You'll learn several alternative approaches to each step, and you'll be empowered to write your own effective ceremonies using sound magical, theological, and pragmatic principles. [via]