The cellular basis of salt tolerance in halophytes depends upon the compartmentation of ions necessary for osmoregulation in vacuoles and upon osmotic adjustment of the cytoplasm by compatible solutes. The central role played by Na+ and Cl− in osmotic adjustment suggests that the transport of these ions and its regulation must be of primary importance in the physiology of the plant as a whole. There have been few investigations into the regulation of leaf ion concentrations, but such data as are in the literature suggest that limiting xylem Na+ (and Cl−) concentrations, together with continued leaf expansion, are particularly important. The role of phloem in retranslocation is uncertain due to lack of data. Decreases in transpiration rate per unit area of leaf help to lower the ion input into leaves. Any linked reductions in photosynthesis appear to be due to decreases in stomatal frequency.