An introduction to the life and ideas of F. M. Alexander, describing and assessing the essential features of his technique of consciously controlling one's body and mind
This is a great history of F.M Alexander and the development of the technique, including the early clinical research into the effects of the method. (Written in 1976, it's a little dated now.) If, however, you are looking for a book about how to do the Alexander Technique, keep looking, since you'll only find a chapter or so that is applicable.