Salt has played an important role in the human diet since earliest times. However, increases in the availability and consumption of dietary salt have raised concerns that excessive intakes may cause hypertension. Although recent research has linked salt intake to variations in blood pressure, definitive conclusions have been lacking. Uncertainties in this area are due to the complex effects of salt on the cardiovascular system and on blood pressure regulation. Nevertheless, many of these complexities are now well understood and have been summarized in this review. Among the topics we examine are the effects of salt on fluid and electrolyte homoeostasis; potential mechanisms of salt-induced hypertension; the epidemiology of salt intake and blood pressure; the effects of salt restriction and supplementation on blood pressure regulation; the potential roles of sodium and chloride ions, as well as interactions with dietary potassium, calcium, and magnesium; current theories of salt sensitivity; the clinical risks of dietary salt depletion; and the dietary sources of salt.