This volume provides comprehensive coverage of all aspects of cosmology and extragalactic astronomy at an advanced level. Beginning with an overview of the key observational results and necessary terminology, it goes on to cover important topics including the theory of galactic structure and galactic dynamics, structure formation, cosmic microwave background radiation, formation of luminous galaxies in the universe, intergalactic medium and active galactic nuclei. Topics are developed in a contemporary fashion, with emphasis on currently active research areas. This self-contained text has a modular structure, and contains over one hundred worked exercises. It can be used alone, or in conjunction with the previous two accompanying volumes (Volume I: Astrophysical Processes, and Volume II: Stars and Stellar Systems). The textbook develops all aspects of extragalactic astronomy and cosmology in a detailed and pedagogical way, and will be invaluable to researchers and graduate students of extragalactic astronomy, astrophysics and theoretical physics.