After studying ring-chain tautomerism of keto ami des and related derivatives of functionalized carboxylic acids for more than ten years, the authors consider it useful to summarize available results on these prototropic equilibria. First attempts to systematize the material were published by Jones in 1963 (Chapter 1, ref. 11). Much, sometimes contradictory, experimental data were scattered about the literature at that time; spectroscopic methods, applied to this field during the last two decades, were needed to revise several previous concepts. In the following years special aspects of ring-chain tautomerism have been discussed occasionally, but no attempt was previously made to cover the whole field. This review is designed to provide a comprehensive compilation of ring-chain tautomerism with one exception: carbohydrates which have already been treated repeatedly, have been omitted. The book is based on a monograph published in Russian: R. E. Valters, Ring-Chain Isomerism in Organic Chemistry. Zinatne. Riga, 1978. There fore, the arrangement and development of the theme is due mainly to one of the authors (R.E.Y.). In the present work the literature has been covered until the end of 1982.