Thermography is a powerful crop phenotyping tool because it enables contactless temperature measurement of the plant or crop canopy. The plant canopy temperature (CT) reflects transpiration and this can be related to yield, as shown in numerous studies on wheat. There are various CT sensing methods that are explained herein. In order to effectively apply thermography as a phenotyping tool, the micrometeorological conditions need to vary as little as possible between the measurement of multiple genotypes. Aerial remote sensing of CT is therefore highly promising for crop phenotyping. This chapter connects the fundamental principles of thermography with its application in crop phenotyping, including discussion of the key technologies, methods and their limitations. Relevant case study examples are discussed.