This review discusses the molecular responses of photosynthesis to moderate heat stress, focusing on the primary targets of thermal damage: the oxygen-evolving complex and associated cofactors in photosystem II (PSII), carbon fixation by Rubisco, and the ATP-generating system. Recent studies suggest that moderately high temperatures do not cause significant PSII damage but inhibit its repair, which involves the de novo synthesis of proteins, particularly the DI protein, due to the generation of reactive oxygen species (ROS). ROS primarily affect the repair system of PSII but do not directly damage the PSII reaction center (RC). Heat stress also induces the cleavage and aggregation of RC proteins, though the mechanisms are unclear. Membrane-linked sensors trigger the accumulation of compatible solutes like glycine betaine and the expression of stress proteins, which alleviate ROS-mediated inhibition of repair and are crucial for acclimation. The review highlights the importance of understanding the balance between damage and repair processes during heat stress to improve plant resilience and productivity.This review discusses the molecular responses of photosynthesis to moderate heat stress, focusing on the primary targets of thermal damage: the oxygen-evolving complex and associated cofactors in photosystem II (PSII), carbon fixation by Rubisco, and the ATP-generating system. Recent studies suggest that moderately high temperatures do not cause significant PSII damage but inhibit its repair, which involves the de novo synthesis of proteins, particularly the DI protein, due to the generation of reactive oxygen species (ROS). ROS primarily affect the repair system of PSII but do not directly damage the PSII reaction center (RC). Heat stress also induces the cleavage and aggregation of RC proteins, though the mechanisms are unclear. Membrane-linked sensors trigger the accumulation of compatible solutes like glycine betaine and the expression of stress proteins, which alleviate ROS-mediated inhibition of repair and are crucial for acclimation. The review highlights the importance of understanding the balance between damage and repair processes during heat stress to improve plant resilience and productivity.