Resistant hypertension (RH) is a condition that confers a high cardiovascular risk to the patient due to both persistent blood pressure elevation and the high prevalence of comorbidities and organ damage. Hypertension is defined as resistant (RH) to treatment when a therapeutic strategy that includes appropriate lifestyle measures plus a diuretic and two other antihypertensive drugs belonging to different classes at adequate doses fails to lower blood pressure (BP) values to < 140 and 90 mm Hg, respectively. Prior to diagnosing a patient as having RH, it is important to document adherence and exclude white-coat hypertension, inaccurate measurement of BP, and secondary causes. Ambulatory BP monitoring (ABPM) has become an important tool in the diagnosis and follow-up of hypertensive patient, and it is even more important in the evaluation of those with resistant RH. Among patients with RH, it is very important to select patients with standardized stepwise screening: ABPM of resistant hypertensives has a circadian profile with a high proportion of nondipping. The possible reasons for the absence of dipping are sleep disturbance, obstructive sleep apnea, obesity, high salt intake in salt-sensitive subjects, orthostatic hypotension, autonomic dysfunction, chronic kidney disease, diabetic neuropathy, and old age. It seems reasonable to routinely use ABPM in the initial evaluation of all resistant hypertensive patients. In a significant number of these patients, ABPM will also be an essential tool in follow-up, especially regarding the possible effects of all therapeutic maneuvers that are devoted to bringing BP into the target ranges. The potential success of other therapeutic options such as renal denervation depends on the ability to select patients most likely to benefit.