"Ye cannot be a witch alone," the Charge of the Goddess goes, but that text meant something different from what many opposed to solitary practice seem to think. You can, in fact, be a witch alone, and Marian Green provides what turns out to be a pretty good sourcebook for those who choose that way.
Green's got some excellent ideas for spiritual practice and attunement that work quite well no matter what your path. Her insistence on exploring the history of the region where you live, for instance, is well merited. Much of what's written about modern witchcraft practice is based on British practice and British folklore, and doesn't fit very well for many who live in the United States and elsewhere. Really learning the properties of various herbs and substances is also a good idea, and much more thorough than following someone else's set of correspondences.
However, I have a few quibbles with this book, the major one being that Green herself is no historian. Her comments on history and folklore often blur one into the other, resulting in errors that anyone who's read a bit of either will spot. This reduces the credibility of her work, which is a shame because so much of it is so good.
Green is emphatically not addressing Wiccans here, or at least not solely Wiccans. That's fine; we Wiccans have enough 101 books to last us until the universe grows cold. Her ideas, though, are interesting no matter what your path, and are useful for those who are Wiccan as well as those who are not.
There are so many beginners' books on Wicca that many Wiccans refer to them as "Wicca 101" books. The information in them is usually very basic, and the ease of reading and how interesting they are depend on the author's personality. But they all say pretty much the same thing. "A Witch Alone" stands out from the others for two reasons. Firstly, it is written in thirteen chapters, each a lesson. At the end of each Ms. Greene gives you a project and a reading list. These have specific goals that open the student up to the mysteries of this ancient religion in an easy, gentle way. While guidance is always preferable, if you have no teacher near you, this is nearly a substitute. Secondly, there is a flexibility about each chapter/lesson that teaches something else -- the ability to use your own intuition, a very important resource to any Wiccan. It helps the person develop a sense of spiritual self, and does so in the most effective way.
I ask my students to use "A Witch Alone" along with with Scott Cunningham's "Wicca: A Guide for the Solitary Practitioner, and Laurie Cabot's "Power of a Witch". The late Mr. Cunningham's book has a wonderfully clear way of organizing the practical things of this religion and some lovely and clear explanations of Wiccan beliefs. Ms. Cabot's book is not only a journey of what it is to be a Wiccan, it is also the only book that talks about the science behind what we call magic.
"A Witch Alone" is a beautiful gift from Marian Greene to those seeking to walk the path of the Wicca.