Infrared, thermography (IRT) is a non-destructive, non-contact method of detecting, gathering and evaluating information about historic buildings. IRT investigation is based on the principle that heat flowing in a material is altered by the presence of anomalies. The changes in heat flow cause localized differences of the surface temperature. By mapping the surface temperature and understanding the heat flow, a map of inner anomalies in the material can be obtained. Four case studies are used to illustrate how, using IRT, information about a building's materials, its condition, characteristics and state of decay can be gathered that may not be evident from visual examination.