Proteins constitute the working-class molecules of the cell. Hence, understanding the way they act is a prerequisite for understanding how a cell functions and how life evolves. Aspects such as the protein-ligand relationship, recognition, protein evolution by point mutation, enzyme-substrate interactions, behaviour of an enzyme in a living cell, control and dynamics of enzyme networks as well as the physico-chemical background of enzyme actions and multi-enzyme complexes are comprehensively treated in this volume.