The book provides an extensive theoretical treatment of whistler-mode propagation, instabilities, and damping in a collisionless plasma. It takes into account different aspects of the electron distribution function, such as temperature, anisotropy, loss cone character and the existence of beams, each of which is of relevance to the study of plasma dynamics, particularly in the conditions of the Earth's magnetosphere. This book fills a gap between oversimplified analytical studies of these waves, based on the cold plasma approximation, and studies based on numerical methods. Emphasis is made on the analysis of relativistic effects on whistler-mode propagation, which has been neglected in most previous studies of this phenomenon. These effects are particularly important in the case of whistler-mode propagation in a rarefied plasma. Consistency between analytical results and the results of numerical analyses confirms the validity of both approaches to the problem.