The effects of the antihypertensive drugs on carbohydrate metabolism and the development of diabetes have been a major research field for more than two decades. Many clinical studies have investigated the effects of the antihypertensive classes on insulin sensitivity and glycemic control, whereas several observational studies and large outcome trials have examined associations of antihypertensive agents with diabetes incidence. In general, thiazide diuretics and conventional beta blockers decrease insulin sensitivity and increase new-onset diabetes, whereas angiotensin-converting enzyme inhibitors, calcium channel blockers, and angiotensin II receptor blockers have neutral or beneficial effects on these parameters. However, several issues in this field, such as the specific properties of newer agents and the relationship of adverse metabolic outcomes and cardiovascular risk, remain to be fully elucidated. This article presents and evaluates the current knowledge in this important area.