The study of the spectra and related characteristics of random and almost periodic operators of various types (Schrodinger, continuous, discrete and more general) is a lively field of research lying at the intersection of mathematical physics, spectral theory of operators and probability theory. A widespread interest in the domain and a considerable amount of mathematical activity have led to many new results and viewpoints yielding insight even into traditional questions. This book by two of the leading researchers is a systematic treatment of the fundamental problems and the large body of mathematical results known. The book also provides a number of exercises illustrating these results to guide the reader towards improvements and generalizations.