Clear evidence shows that decreasing blood pressure reduces risks for major cardiovascular events in patients with hypertension. However, there is considerable uncertainty about the separate effects of the various classes of blood pressure-lowering agents and the effects of blood pressure lowering in patients at high risk, particularly in the absence of hypertension. Several new randomized controlled trials have been started in the past few years in an effort to address these questions. However, individually, these studies are unlikely to resolve all current uncertainties. For this reason, systematic overviews and meta-analyses of the major ongoing trials are planned. The overviews will be conducted as a collaboration among the principal investigators of the participating trials and will involve about 270,000 patients and 1.1 million patient-years of follow-up. The combined trial results should provide good statistical power to detect even modest differences in the effects of various treatments on major cardiovascular outcomes.