Graduate students and researchers in astrophysics and cosmology need a solid grasp of a wide range of physical processes. This authoritative textbook helps readers develop the necessary toolkit of theory. The book is modular in design, allowing the reader to pick and chose a selection of chapters, if necessary. It carefully develops a solid understanding of radiative processes, spectra, fluid mechanics, plasma physics and MHD, dynamics of gravitating systems, general relativity, nuclear physics, and other key concepts. Throughout, the reader's understanding is developed and tested with problems and helpful hints.