One of the first things that everyone will notice about our thermal imaging cameras and infrared thermometers is that the emissivity capabilities are defined for every single product. Emissivity is either fixed - typically at 0.95 - or adjustable at varying increments between 0.1 and 1 in most thermal imaging cameras. This article aims to explain what emissivity is, how it is determined, and the practical challenges it presents for thermographers and technicians.