Enzymes are giant macromolecules which catalyse biochemical reactions. They are remarkable in many ways. Their three-dimensional structures are highly complex, yet they are formed by spontaneous folding of a linear polypeptide chain. Their catalytic properties are far more impressive than synthetic catalysts which operate under more extreme conditions. Each enzyme catalyses a single chemical reaction on a particular chemical substrate with very high enantioselectivity and enantiospecificity at rates which approach ?catalytic perfection?. Living cells are capable of carrying out a huge repertoire of enzyme-catalysed chemical reactions, some of which have little or no precedent in organic chemistry. The popular textbook Introduction to Enzyme and Coenzyme Chemistry has been thoroughly updated to include information on the most recent advances in our understanding of enzyme action, with additional recent examples from the literature used to illustrate key points. A major new feature is the inclusion of two-colour figures, and the addition of over 40 new figures of the active sites of enzymes discussed in the text, in order to illustrate the interplay between enzyme structure and function.