In October 1978, a group of 41 scientists from 14 countries met in Erice, Sicily to attend the Second Course of the Interna tional School of Radiation Damage and Protection "Ettore Majorana", the proceedings of which are contained in this book. The countries represented at the School were: Brazil, Canada, Federal Republic of Germany, Finland, German Democratic Republic, Hungary, India, Italy, Japan, Spain, Sweden, Switzerland, United States of America, and Yugoslavia. The School was officially sponsored by the Italian Health Physics Association, the Italian Ministry of Public Education, the Italian Ministry of Scientific and Technological Research, and the Sicilian Regional Government. In addition, administrative and tech nical support was received from the Stanford Linear Accelerator Center and from CERN. The past 15 or so years have witnessed a significant develop ment of computer methods in the science of radiation protection. The radiation transport codes associated with hadronic and electro magnetic cascades, reactor shielding, unfolding techniques, and gamma ray spectrum analysis have reached the state-of-the-art level, and the Erice Course aimed at presenting as comprehensive an over view of these programs as was possible within the allotted time span.