Hypertension is a major risk factor for cardiovascular and renal disease, and a leading cause of premature mortality worldwide. Early hypertension studies showed that treating elevated blood pressure (BP) reduces patients' risk of cardiovascular disease and all-cause mortality. In subsequent research, patients achieved greater improvement in cardiovascular outcomes when their treatment was aimed at a moderate systolic BP target (<150mmHg) than at higher targets. Although observational data suggest that even lower BP targets may be beneficial, this has not been seen in randomized trials; instead, intense treatment of hypertension (i.e., to a target systolic BP <120mmHg) was found to have no effect on participants' risk for renal disease, cardiovascular disease, or all-cause mortality. One potential explanation for this apparent lack of benefit of intense BP targets is that the study protocols targeted reductions in clinic BP rather than ambulatory BP. Ambulatory BP monitoring (ABPM) allows for assessment of BP throughout the day and night. Of all the BP measurements, nighttime systolic BP appears to be the best predictor of cardiovascular disease and all-cause mortality. Because recent trials assessing intense BP targets did not include ambulatory BP measurements, the effect of intensive treatment on nighttime BP is largely unknown. To address this important gap in knowledge, we will conduct ABPM in 950 participants as part of an ancillary study to the ongoing Systolic Blood Pressure Intervention Trial (SPRINT). The goal of the ancillary study is to evaluate the effect of intensive vs. standard clinic based BP targets on nighttime BP (primary outcome), as well as night/day BP ratio, timing of peak BP, 24hr BP, and BP variability (secondary outcomes). Regardless of the outcomes, completion of the proposed ancillary study will significantly impact the direction of future hypertension research. If intensive treatment of BP is associated with lower nighttime BP, then results from the parent SPRINT study will demonstrate the effect (positive or negative) of achieving lower nighttime BP on important cardiovascular and renal outcomes. Alternatively, negative overall SPRINT results coupled with an ancillary study finding of no difference in nighttime BP between the groups will indicate the need for future trials to determine whether lowering nighttime BP reduces the risk for CKD progression, end-stage renal disease, and cardiovascular disease. In addition, the proposed study will provide mechanistic insight into the primary SPRINT results by elucidating the effect of intense clinic BP targets on dipping, the timing of peak BP, and BP variability. Lastly, this ancillary study will provide the principal investigator with leadership experience within a large, ongoing clinical trial, thereby preparing the candidate for a career as an independent clinical researcher, with the long- term goal of reducing the morbidity and mortality associated with hypertension through therapies targeted to specific components of ambulatory BP.