Ambulatory blood pressure (ABP) has long been recognized by researchers as the gold standard of blood pressure (BP) measurement. Researchers and clinicians typically rely on the mean measure of ABP; however, there is considerable variability in the beat-to-beat BP. Although often ignored, this variability has been found to be an independent predictor of cardiovascular disease and mortality. The aim of this paper is to provide a conceptual review of ABP variability (ABPV) focusing on the following: associations between ABPV and health, whether ABPV is reliable, how to calculate ABPV, predictors of ABPV, and treatments for ABPV. Two future directions are discussed involving better understanding ABPV by momentary assessments and improving knowledge of the underlying physiology that explains ABPV. The results of this review suggest that the unique characteristics of ABPV provide insight into the role of BP variability in hypertension and subsequent cardiovascular illness.