This text provides a modern alternative to other introductory nuclear engineering textbooks that have not been significantly updated over the last 20 years. It covers topics of interest to the modern nuclear engineer as well as anyone seriously interested in pursuing a long-term career in the field of nuclear science and engineering. The subject matter is sufficiently broad to meet the needs of both junior and senior undergraduates, but it is advanced enough to meet the needs of first- and second-year graduate students.