Vitamin D has been known to medical science for almost a century. Yet, it is only in the last 15 years that we have realized that the biological effects of vitamin D extend far beyond the control of calcium metabolism. Recent observational evidence suggests strong links between low vitamin D levels and a range of cardiovascular conditions, including stroke, myocardial infarction, hypertension, and diabetes. Interventional studies are beginning to explore whether vitamin D supplementation can modify vascular health and prevent cardiovascular disease. This article reviews the physiology and function of vitamin D, examines the current observational and intervention data in cardiovascular disease, and discusses future research and current practice recommendations.