This book describes the principles of Endor spectroscopy and Triple resonance, with particular emphasis given to applications in organic chemistry and biochemistry. It gives a broad survey of Endor studies of organic and bioorganic radicals in solution, but also discusses in detail special topics such as non-proton Endor, multispin systems, dynamic effects, and Endor spectroscopy using liquid-crystal solvents. Although the authors have adopted a phenomenological presentation for the most part, they also provide a sound theoretical basis. The theoretical concepts and wealth of experimental material presented illustrate the scope and limitations of the different multiple resonance techniques and facilitate finding optimum experimental conditions for a given problem.