In photosynthesis Rubisco catalyses the assimilation of CO ₂ by the carboxylation of ribulose-1,5-bisphosphate. However, the catalytic properties of Rubisco are not optimal for current or projected environments and limit the efficiency of photosynthesis. Rubisco activity is highly regulated in response to short-term fluctuations in the environment, although such regulation may not be optimally poised for crop productivity. The regulation of Rubisco activity in higher plants is reviewed here, including the role of Rubisco activase, tight binding inhibitors, and the impact of abiotic stress upon them.