Blood pressure (BP) variability describes the degree to which BP measures are dispersed during a specified time frame. Studying the prognostic significance of BP variability is challenging owing to the myriad options for the time frame used to define it. At one end of the spectrum, very short-term BP variability describes beat-to-beat or minute-to-minute variation, such as when using BP measured continuously using an intra-arterial catheter. At the other end of the spectrum, long-term BP variability describes variation over a period of months or years, such as when using BP measured during periodic clinic or study visits.