One might wonder if there is really a need for another book on plate tectonics. Many books exist on this topic already, and the field has reached a stage of maturity where some good books (i.e., books that I have found useful) are already out of print. This is the concern I had when I sat down with this book; however, I was quickly won over by both the content and structure. Davies attempts to separate well-established observations and physical principles things known with a reasonable degree of certainty from interpretation and theory, where the application of these principles is less certain. He walks this fine line well, with a few exceptions.