Embryonic stem (ES) cells are a rich source of multiple different cell types of diverse lineages. Significant advances have recently been made in our understanding of the molecular mechanisms by which ES cells differentiate into endothelial cells. The differentiation of ES cells into endothelial cells can be enhanced by certain growth factors, environmental cues, cell-cell interactions, and extracellular matrix. A wide variety of signal transduction pathways and transcription factors have been shown to participate in this process. The use of ES cells for endothelial differentiation are not only of interest with respect to the molecular mechanisms but also for identifying sources of endothelial cells that can be used for a number of therapeutic purposes. The purpose of this chapter is to review recent advances in the molecular mechanisms underlying ES differentiation into endothelial cells and how endothelial cells derived from ES cells are being used therapeutically.