A state is approached in the knowledge of the structure of proteins and of the function of proteolytic enzymes wherein the understanding of the complex interactions involved in the proteolysis of native proteins will be possible. This book has been written with the purpose of presenting these relationships as they appear at the present time. Naturally, the potentials of the complete stereochemical structure of an ever increasing number of proteolytic enzymes, has not yet been fully exploited. A few years from now the picture will become much clearer.