On behalf of the IAU Commission 48 "High Energy Astrophysics" a special session on "CNO Isotopes in Astrophysics" was held at the General Assembly of IAU in Grenoble on August 30, 1976. This topic was chosen since it has recently included many exciting developments in various domains of physics and astrophysics such as for instance meteoritical studies, radioastronomy measurements of the interstellar gas, new determinations of nuclear reactions cross-sections and fractionation processes. The papers of this volume are the written versions of the talks which were presented during this session and cover the most recent observations and theoretical developments re­ garding this fast-growing field. Let me thank first Professor Martin Rees (Institute of Astronomy at Cambridge) the chairman of IAU Commission 48, who has sponsored this special session and made it possible. I am indebted to the authors of the papers for their contributions and all the work they have put in the excellent presentation of the material. lowe special thanks to Professor William A. Fowler (Kellogg Laboratory at Cal tech) who has superbly chaired this session and made it very exciting and lively, to Professor Beatrice M. Tinsley (Yale University) who accep­ ted the difficult task to conclude and sGmmarize on such a burning and moving topic, and to Dr James Lequeux for his invaluable help in the edition of several contributions. Finally, the edition of this book would not have been possible with­ out the skilled and generous aid of Miss Jeannette Caro.