The initial impetus for this text occurred when we were searching for a single book that could be recommended to the attendees at the Mossbauer Spectroscopy Institute at The Catholic University of America. This Institute is an introductory course on the theory and interpretation of Mossbauer spectroscopy for workers in industrial, academic, and government labora tories. None of the books available adequately covered the breadth and scope of the lectures in the Institute. A list of these books and review articles is included in Appendix C. To meet our needs, we undertook the creation of this text. The chapters are based upon the lectures given at the various Institutes from 1967 to 1969. Most of the lectures were recorded and transcripts sent to the lecturers, who then prepared the manuscripts, using the transcripts as a guide so as to retain the style developed during the lecture. Each chapter is written in the style of the authors. As the editor, my main task was to main tain uniformity of format and nomenclature. A list of nomenclature used in this volume is reproduced in Appendix A. We hope that this list will be used particularly by new investigators and teachers of Mossbauer spectroscopy so that future literature will employ a uniform system.