The book "Reactor Technology" describes the physical and technical fundamentals and their concrete implementation in power plants. After presenting the nuclear physics and thermohydraulic foundations, the authors describe the basic principles and structure of established reactor concepts as well as new developments. Another focus is on operational, material, and reliability issues. Finally, the authors address the fuel cycle from uranium mining to disposal. The motivation of the editors was to compile the current state of knowledge in reactor technology and make it accessible to engineers in both study and practice. The book is based on the standard work of reactor technology edited by Albert Ziegler. It is suitable not only as a textbook for students but also as a reference work for professional practice.