Operational Caharacteristics of Infrared Photodetectors.- Impurity Germanium and Silicon Infrared Detectors.- InSb Submillimeter Photoconductive Detectors.- Far-Infrared Photoconductivity in High Purity GaAs.- Avalanche Photodiodes.- The Josephson Junction as a Detector of Microwave and Far-Infrared Radiation.- The Pyroelectric Detector--an Update.