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Hypertensive emergencies are life-threatening conditions because their course is complicated with acute target organ damage. They can present with neurological, renal, cardiovascular, microangiopathic hemolytic anemia, and obstetric complications. After diagnosis, they require the immediate reduction of blood pressure (in <1 hour) with intravenous drugs such as sodium nitroprusside, administered in an intensive care unit. These patients present with a mean arterial pressure >140 mm Hg and grade III to IV retinopathy. Only occasionally do they have hypertensive encephalopathy, reflecting cerebral hyperperfusion, loss of autoregulation, and disruption of the blood-brain barrier. In hypertensive emergencies, blood pressure should be reduced about 10% during the first hour and another 15% gradually over the next 2 to 3 hours to prevent cerebral hypoperfusion. The exception to this management strategy is aortic dissection, for which the target is systolic blood pressure <120 mm Hg after 20 minutes. Oral antihypertensive therapy can usually be instituted after 6 to 12 hours of parenteral therapy. Hypertensive urgencies are severe elevations of blood pressure without evidence of acute and progressive dysfunction of target organs. They demand adequate control of blood pressure within 24 hours to several days with use of orally administered agents. The purpose of this review is to provide a rational approach to hypertensive crisis management.