The present volume contains the proceedings of the 23rd Mos- bach Colloquium on "Protein-Protein Interactions". It includes the paper by Prof. S. LIFSON who unfortunately was unable to attend. Discussions were included whenever possible in order to make the complete proceedings accessible to the future reader. The colloquium was generously supported by the firms who are corporate members of the Gesellschaft fur Biologische Chemie. Dr. W. B. GRATZER and Dr. L. JAENICKE, as weIl as some of the invited speakers, were a tremendous help in preparing the program and we wish to thank them for their...