General considerations in the field of remote sensing are discussed, particularly geological applications of infrared measurements. The theory of electromagnetic radiation as described by Planck's law is briefly reviewed. IR scanning and radiometry are the most commonly used techniques. Scanning provides photographic images of the spatial distribution of surface radiation. This technique was first used in Italy to obtain radiation data at Solfatara di Pozznoli. The primary causes of error in the technique are variable atmospheric transmissivity, angular inclination, and variable emission. Problems involved in calibration are discussed. The data derived from surveys of volcanic regions are presented in tables and the thermal images and maps are provided. This technique is useful in surveying volcanoes and for the detection of high temperature geothermal resources.