Resistant hypertension is defined as failure to achieve goal blood pressure despite adherence to 3 different antihypertensive medications, one of which must be a diuretic. True resistant hypertension must be distinguished by apparent resistant hypertension, of which an important cause is medication nonadherence, which can be recognized through a variety of monitoring strategies and may be improved through better patient education. A thorough history and examination should focus on evaluating for associated factors such as medication and illicit drug use, alcoholism, obesity, and obstructive sleep apnea. Further evaluation to differentiate apparent resistant hypertension from true resistant hypertension should include consideration of ambulatory blood pressure monitoring to rule out white coat hypertension. Routine laboratory work will reveal chronic kidney disease, which is the most common associated factor in resistant hypertension. Secondary or identifiable causes of resistant hypertension include primary aldosteronism, renovascular disease, and pheochromocytoma. Diagnostic evaluation for identifiable causes should be tailored for each patient and guided by signs and symptoms, as well as risks and benefits.