Respiration is vital; it is the essence of life. Respiration is the mechanism by which energy obtained during the photosynthesis process is transformed into biochemical energy, in the form of ATP. This transformation of energy keeps all cells in all organisms alive. While energy conversion is the main function of respiration in animals, respiration has several other functions in plants. Among them, interactions with photosynthesis such as photorespiration and the production of carbon skeletons for the many compounds synthesized in plants (e.g., pigments, proteins and secondary metabolites). Therefore, it comes as no surprise that such a key role of respiration in plants promoted intense effort to investigate its regulation. Nevertheless, the interactions with other simultaneous processes make its measurement in plants very challenging. In animals, respiration can be simply measured as CO2 or O2 exchange with the atmosphere since there are no other processes performing similar gas exchange. In contrast, in plants, respiration produces CO2 and consumes O2 simultaneously with photorespiration.