Sucrose is generally considered the primary photosynthate in plants; however, many horticultural crops, including rosaceous fruit trees, synthesize and use polyols (sugar alcohols). This review describes recent progress in physiological research on the metabolism and transport of sorbitol in rosaceous fruit trees, and of mannitol, another common polyol, in horticultural crops. Studies on various polyols other than sorbitol (in rosaceous fruit trees) and mannitol are then described. Polyols play a role not only in the translocation and storage of photosynthates but also in biotic and abiotic responses in many horticultural crops; therefore, this review also provides insights into the effects of polyol metabolism on the biochemical mechanisms of pathogenicity and environmental stress tolerance, including a novel strategy for engineering stress tolerance.