Alan Fersht has revised his classic text Structure and Mechanism (Freeman, 1985) and extended it to include applications of the protein engineering method to characterizing transition states in protein folding and enzyme catalysis. His earlier textbook was so good it scared off possible competitors, and its notable features are preserved in the new text. It provides enough information about techniques to make close connections between discussions of mechanism and actual data. It packs an amazing amount of information and viewpoint into a short space without losing readability. It does not just derive equations, it explains their physical meanings and it aims to develop the reader's physical insight. The assumptions behind an approach are laid out clearly and, when a topic is controversial, the author gives his own viewpoint at the end. The pace of research today is such that few leading scientists find time to write textbooks, and the scientific community is surely grateful to Alan Fersht for revising his. However, as he points out, a main section of the book covering classical enzymology has not been revised.