This expanded new edition develops the theory of nuclear reactors from the fundamentals of fission to the operating characteristics of modern reactors. The first half of the book emphasizes reactor criticality analysis and all of the fundamentals that go into modern calculations. Simplified one group diffusion theory models are presented and extended into sophisticated multi-group transport theory models. The second half of the book deals with the two main topics of interest related to operating reactors – reactor kinetics/dynamics, and in-core fuel management. Additional chapters have been added to expand and bring the material up-to-date and include the utilization of more computer codes. Code models and detailed data sets are provided along with example problems making this a useful text for students and researchers wishing to develop an understanding of nuclear power and its implementation in today's modern energy spectrum.