Creation, detection, and manipulation of spin degrees of freedom of electrons and nuclei, phenomena of spin relaxation, decoherence and dephasing, and processes of spin transfer between different subsystems are among the most important problems studied in semiconductor spintronics. These effects are most pronounced in systems with localized charge carriers, such as semiconductor quantum dots. This chapter contains the motivation behind and a brief review of the material presented in the book. It also clarifies the logic of the presentation in further chapters. Chapter 1 may be helpful to readers willing to find appropriate material without going through the whole book, as it contains a concise overview of the other chapters.