This book covers the basics behind thermal hydraulics. It explores the characteristics of power reactors, thermal design principles, and how reactors generate heat. The text also presents transport equations for single- and two-phase flows. The authors discuss the thermodynamics of nuclear energy conversion systems, including nuclear power plants and a simplified power system. They also consider the thermal analysis of fuel, single-phase fluid mechanics and heat transfer, and two-phase flow dynamics and heat transfer. The final chapter presents a steady-state analysis of a single heated channel. A solutions manual is available for qualifying instructors.