Ambulatory blood pressure recordings supply information on the blood pressure variation during habitual daily activities and sleep. Whether the circadian blood pressure curve is modulated by an endogenous clock or whether the diurnal fluctuations in blood pressure are mainly or exclusively determined by the pattern of activity remains disputed. Whatever the underlying mechanism, most experts agree that it still remains to be ascertained whether the blood pressure profile can help in unraveling the pathophysiology of hypertension and determining a subject's cardiovascular risk. The methods for parametrizing the diurnal blood pressure curve in individual subjects, summarized in this article, may provide summary statistics for larger groups of individuals or for the population at large.