This book is based on two keywords: Bioradical and ESR. Bioradical is a newly coined word which encompasses paramagnetic species in biological systems, such as active oxygen radicals and transition metal ions. Research on the structure and function of bioradicals has been attrac­ ting growing attention in the field of biological science, and comprehensive investigations from many fields are helping to understand the real features of these species. ESR spectroscopy also has interdisciplinary features in that its techniques have been applied to many fields, ranging from physics to medicine. It was our hope, therefore, that this book would help to clarify many aspects of bioradicals and that significant progress would be achieved in combining basic research from many different fields. This book arises from the First International Conference on Bioradicals Detected by ESR Spectroscopy (ICBES), which was held in Yamagata, a city in the Yamagata Prefecture of Japan, in 1994. About 300 participants from 16 different countries attended this conference, and about 170 papers were presented. This book is a collection of contributions from the conference and also contains eleven chapters selected by the editorial board, based on sugges­ tions from the members of the international editorial board of ICBES. The Yamagata Technopolis Foundation is developing a biomedical technology for the 21st century based on life science fused with material and physical science. Based on such a techno­ logy, the Foundation plans to share its fruits all over the world.