This book presents the historical background as well as the up-to-date developments in, and guidelines for, bioradicals and ESR research. Bioradicals Detected by ESR Spectroscopy is a newly coined term which encompasses paramagnetic species in biological systems, such as active oxygen radicals and transition metal ions. Research on the structures and functions of bioradicals have been attracting growing attention in the biological sciences, resulting in an increasing demand for comprehensive studies which allow researchers from many fields to understand the true importance of these species. ESR spectroscopy is of great interest to interdisciplinary research and is applied in many fields, ranging from physics and chemistry to biology and medicine. New ESR technologies of multiquantum ESR, STM-ESR and open-space ESR, several ESR imaging techniques, spin trapping and new methods in in vivo spin trapping are all described and discussed in this volume. In addition, it demonstrates the applications of ESR in food and medical sciences, i.e., the estimation and characterization of the antioxidant ability of foods and food components and the elucidation of the underlying chemical mechanisms.