This book presents a detailed account of one of the most mysterious problems in science — whether ordinary magnetic fields can exert an appreciable influence on chemical and biochemical reactions. The first aim of the book is to introduce this research, through theoretical and dynamic spin chemistry, to graduate students and researchers, by means of detailed theoretical and experimental descriptions. The second aim is to review typical recent investigations, which will stimulate new interest and applications in the 21st century. Because dynamic spin chemistry is based on established science, it is expected to provide a guide for all situations in which radicals, radical pairs, and higher spin species occur, including the effects of environmental electromagnetic fields on the human body.