Foreword. Historical background. Revision of radiometry. Origins of infrared radiation. Thermal emission by matter. Transmission by the atmosphere. Optical materials for the infrared. Optical image formation. Scanning and imaging, Spectral filtering. Radiation detectors. Signal processing. Characterization of infrared systems. Imaging and measurement. Choosing the spectral band. Industrial and military applications. Infrared spectroradiometry. Line scanners. Advances in thermographic systems. Bibliography. Plates.