Photosynthesis is essential to life on earth, yet photosynthesis converts sunlight to biomass with relatively low efficiency. Several promising strategies have been proposed for improving photosynthetic efficiency, and the recent implementation of some strategies demonstrates a capacity for increasing CO2 assimilation and yield in both model plants and staple crops. Recent developments in photosynthesis research emphasize conducting photosynthesis measurements under both steady-state and fluctuating environmental conditions, using phenotyping tools to enable rapid detection of photosynthetic rates, and quantifying gaseous fluxes from the leaf to the canopy level for a more comprehensive picture of photosynthetic processes. A greater understanding of photosynthesis will enable new opportunities for breeding and biotechnology advances. Thus, this Methods Collection describes techniques used to modify and measure photosynthesis from the molecular to canopy scale in model and crop plants grown in controlled and field settings.