SummaryLeaf day respiration (Rd) strongly influences carbon‐use efficiencies of whole plants and the global terrestrial biosphere. It has long been thought that Rd is slower than respiration in the dark at a given temperature, but measuring Rd by gas exchange remains a challenge because leaves in the light are also photosynthesizing. The Kok method and the Laisk method are widely used to estimate Rd. We highlight theoretical limitations of these popular methods, and recent progress toward their improvement by using additional information from chlorophyll fluorescence and by accounting for the photosynthetic reassimilation of respired CO2. The latest evidence for daytime CO2 and energy release from the oxidative pentose phosphate pathway in chloroplasts appears to be important to understanding Rd.