This is the first of several AGARDographs commissioned by the Fluid Dynamics Panel to deal with instrumentation techniques used in hypersonic short-duration facilities and with related topics. Since one of the reasons for the development of such facilities was the need for experimental data on the extremely high heat-transfer rates that a body experiences in re-entry conditions, the measurement of heat transfer constitutes a particularly appropriate initial subject area moreover, the methods to be described are also applicable to a variety of problems other than those of hypersonic flow. An important feature of this AGARDograph is the unified treatment that it accords to the theory underlying heat-transfer gauges of various types. In addition, a detailed analysis is given of the magnitude of the errors in the values of heat-transfer rate deduced from the observations. Constructional considerations are discussed fully physical data and design charts are included.