The report is intended to give practical assistance to all instrumentation and test engineers working in the field of temperature measurements in aircraft at Mach numbers up to 2.3 and altitudes up to 80,000 feet. After a general discussion of the requirements of aircraft temperature measurements, and the available temperature sensing technology, the detailed techniques of using resistance probes and thermocouples, as well as the associated electrical leads, circuits, and indicators, are explained. A discussion of heat transfer processes, primarily between moving fluids and solids, includes terminology, the systematics of temperature measurements, and the concept of total temperature as the main operational parameter. An extensive section deals with errors in temperature measurements, as functions of various parameters, in gases, liquids and solids. Typical laboratory and in- flight calibration techniques for thermometers are described, followed by discussions of data handling, error analysis, and the limits of present methods.