In patients with uncomplicated essential hypertension, cardiac output remains within normal ranges and intravascular volume is normal or low, assuming the presence of a sufficient Windkessel effect and usual resistance and compliance calculations. However, mean circulatory pressure is elevated in these patients. In addition, vascular resistance is augmented, and most importantly, the viscoelasticity of the cardiovascular system is substantially impaired. Such considerations are essential to understanding the mechanisms behind carotid-femoral arterial stiffness, a major risk factor in individuals with hypertension. Arterial stiffness, measured from pulse wave velocity, is substantially increased in hypertension even independently of blood pressure levels. Structural vascular changes and endothelial dysfunction are consistently associated with vessel impairments in animal models of hypertension. Increased arterial stiffness has a major effect on pulse pressure (the difference between systolic and diastolic blood pressure), wave reflections, kidney function, and above all, cardiovascular risk. This increased cardiovascular risk is particularly deleterious in patients with hypertension and/or type 2 diabetes mellitus, who are at risk of both renal and cardiovascular events. In this Review, we discuss the importance of arterial stiffness in the diagnosis and management of hypertension and the need for new approaches for the treatment of hypertension in patients with or without diabetes and/or renal impairment.