The intention of this chapter is to trace the origin of infrared thermography (IRT) and to supply its theoretical basis. The speech goes through the milestones by eminent scientists and is supported by the most important basic relationships. The reader is also plunged into radiation mechanisms which are fundamental as starting points for comprehension and then application of infrared thermography. A section is devoted to detector’ technology with a description of the basic features, which should be taken into account for the choice of the most appropriate equipment for the specific application. The main historical steps in detector’ development are also traced owing to the dynamic evolution of the infrared devices. Indeed, following the technological progress, the performance of infrared devices improves ever more, leading to novel applications.
Keywords: Infrared thermography, origin of infrared thermography, basics of infrared radiation, radiation mechanisms, technology of infrared detectors, infrared detectors performance, behavior of materials in the infrared spectrum, materials emittance, surface emissivity.