Heat is utilized in machines and process engineering systems, in thermal energy technology, and in building physics, or it must be removed from systems where it causes disturbances. This textbook deals with heat transfer and temperature fields and their calculation. The first part provides a practical introduction and is oriented towards problem statements typical for mechanical engineering, process engineering, and building physics. Subsequent chapters delve into heat exchange at interfaces and the calculation methods for steady-state and unsteady heat transfer. The appendix contains a comprehensive directory of thermophysical material values needed for practical work.