Block copolymers (macromolecules of two or more chemically distinct blocks) exhibit rich phase behavior, which has made them attractive for the design of novel polymer materials as well as for studies of self-assembly. This book provides a coherent, single source for the theoretical understanding of block copolymer self-assembly, and an introduction to the theory of phases and phase transitions in soft matter. It emphasizes self-consistent field theory, which provides a semi-quantitative description of the phase behavior of block copolymer melts and blends, while also surveying other approaches. The author also discusses technological applications and numerical methods.