C4 crops such as maize and sorghum are vital to global food and bioenergy systems due to their high productivity and resource use efficiency, underpinned by a CO2 concentrating mechanism. Despite this advantage, modelling and experimental evidence indicate that C4 photosynthesis can be further optimised to boost yield and carbon capture. This review examines key metabolic and physiological processes predicted to limit C4 photosynthetic flux by the steady-state and dynamic models, including the activity of carboxylases, electron transport, and mesophyll and bundle sheath (BS) conductance. We highlight recent progress using Setaria viridis and model crops to test genetic strategies for alleviating these limitations. In addition, we explore promising but less-understood areas, such as enhancing light-harvesting and adenosine triphosphate (ATP) generation in BS cells, improving metabolite exchange and activating alternative decarboxylation pathways under stress. We suggest that improving C4 photosynthesis will require coordinated manipulation of multiple biochemical and regulatory processes. Advancing our understanding of these processes will not only enhance C4 crop productivity and resilience but also support long-term goals of engineering C4 traits into C3 crops to address rising demands for food, energy, and climate adaptation.