I've read several books on Voice Pedagogy and this is clearly the best one. James McKinney, the author, is a former student of William Vennard, a great voice teacher and voice pedagogue.
McKinney treats his book in a somewhat similar way that the MD might treat a patient (though, naturally, there are many differences between the M.D. and the voice teacher). I especially like McKinney's concept that the observation begins as soon as the student walks in the door. How do they stand? Talk? Act?
McKinney's chapters cover all the right areas of vocal production all in the right order: posture, breathing and support, phonation, registration, voice classification, resonation, articulation, the speaking voice, and coordination.
What I really like about the book is that McKinney dispenses with all the mumbo-jumbo of some voice books and gets right to the point. During each chapter, he notes the various problems associated with each chapter heading (problems relating to vowels which are too dark) and gives several concrete options for fixing the selected problem. If there are things McKinney doesn't know about (such as the exact cause of vibrato), he states the latest theories and scientific evidence, gives his personal opinion from his experience, and states that he doesn't really know. He does all this as well in a very clear fashion.
There are two things I don't like about this book, and I must say that they're not extremely significant. First, McKinney uses phonetic symbols instead of IPA symbols. Also, he doesn't have a conclusion. The book stops abruptly at the end.
But these aren't "dealbreakers." If I had to recommend voice pedagogy books, this would be one of the first, along with books by Clifton Ware, Oren Brown, and Richard Miller (good but more technical).