The role of vascular endothelium in cardiovascular disorders is well recognized. Mature endothelial cells contribute to the repair of endothelial injury, but only with a limited capacity. This has led to growing interest and further investigation into circulating endothelial progenitor cells (EPCs) and their role in vascular healing, repair and postnatal neovascularization. Recent studies have shown that EPCs are affected both in number and function by several cardiovascular risk factors as well as various cardiovascular disease states. Here, we aim to provide an overview of EPCs in humans, from methods of assessment to quantification and functional properties in numerous cardiovascular conditions. In addition, we hope to offer some perspective on the potential diagnostic and therapeutic aspects of EPCs.