This book provides a complete introduction and overview to the rapidly expanding field of extrasolar planets and brown dwarfs. The following topics are covered: observational techniques, surveys, studies of individual objects, theoretical properties of low-mass stars, brown dwarfs and giant planets, the contribution of these objects to the Galactic mass-budget, processes that lead to formation of planets versus white dwarfs, implication of such objects for the occurrence of Earth-like planets, and future prospects in the field. The book enables readers to gain a solid scientific background in all the essential aspects of this exciting new area of astronomical research.