This book is intended to be an introductory text for engineers and physicists who are likely to be involved in the area of optical fiber communications. Its purpose is to provide the student with an explanatory text that can al so be used for "self-study." Thus, key theoretical resul ts have been rather thoroughly derived, and detailed explanations have been given wherever cer tain steps have been excluded. Some of the derivations are in new form, which the reader will hopefully find stimulating. In addition, some of the ex perimental and theoretical results are based on the research of the authors, and they are published here for the first time. However, references are given for all those cases involving equivalent results obtained by others. Although a large number of monographs are available for the specialist or the knowledgeable scientist, most of these are inadequate for teaching pur poses. This aspect served as a major motivation for writing a book that ex plains the basic phenomena and techniques. The required material was partly developed in earlier courses on integrated optics and optical fiber commu nications, and partly resulted from the authors' close cooperation with in dustry. To assess the suitability of the material, the manuscript of the book was used with encouraging results for a graduate course (spring sem ester, 1980) at the Communications Laboratory of the Helsinki University of Technology."