For a long time, enzymes have been studied by measuring their activity, which has led to the advancement of "enzyme kinetics." In recent years, the mechanism of enzyme reaction has been explained in detail on the basis of the 3D structure. Genetic engineering and the 3D structural analysis of enzymes contribute to these advancements in enzymology. This book starts with an introduction to various enzymes to show how interesting enzymes are, which is followed by historical kinetic studies on enzymes and the overall and rapid-reaction kinetics. The subsequent topics describe the basics of protein structure, the control of enzyme activity, and the purification of enzymes. A case on the kinetic and structural studies of l-phenylalanine oxidase is also presented. There are many good books on enzyme kinetics, but few describe their kinetic and structural aspects. This book deals with both and contains many references that can be good sources for further reading. It is handy and is especially helpful for beginners. A number of figures, including some with stereo expression, facilitate observing the 3D structure of enzymes.