Intended as an introduction to magnetic resonance, but equally useful for physics majors, this book is designed primarily for first-year chemistry graduate students and advanced senior undergraduates. The chief claim is to present, in a clear and concise manner, the most important principles and applications of the two kinds of magnetic resonance: nuclear magnetic resonance (N.M.R.) and electron spin resonance (E.S.R.), both of which depend upon the same fundamental principles.