In 1906, Hermann Leuchs, a student of Emil Fischer, discovered the class of N-Carboxy-aminoacid-anhydrides, also known as Leuch's anhydrides, or abbreviated NCAs. These compounds are, even 80 years after their discovery, valuable intermediates in organic synthesis due to their reactivity: NCAs polymerize with the elimination of carbondioxide to yield polypeptides, model compounds for proteins. They can be used as starting material for a variety of pharmaceutically interesting products and for synthetic polymers (fibres and films). Ralph Hirschmann demonstrated the step by step synthesis of ribonuclease utilizing NCAs as monomers. The author of this monograph, Hans R. Kricheldorf, University Hamburg, is, on account of his own research in Freiburg and Hamburg, predestined to give the reader an insight into the organic chemistry of NCAs and related heterocycles as well as macromolecular chemistry, that is the synthesis of polypeptides and the structure-reactivity relationship. I predict a good accept- ance of this book about the class of cyclic aminoacid derivatives by scientists in various areas. Aachen, September 1986 Helmut Zahn Acknowledgment The author would like to express his gratitude to the american chemical society, the royal society of chemistry, Marcel Dekker Inc., John Wiley & Sons, Hiithig & Wepf Verlag and Kobunshi Gakkai for the permission to reproduce figures from their journals.