General Description of a Linear Accelerator and its Component Systems; Basic Processes in Electron Acceleration - the Accelerating Waveguide; The Accelerating Waveguide and its Supply Circuits; The Treatment Head; The Dose Monitoring and Control System; Beam Direction and Beam Shaping Devices; Mechanical Systems; Control and Interlock Systems; Specification and Performance Testing; Accelerator Operation; The Design of Treatment Rooms; Simulators; Conclusions