© 2015 Elsevier Inc. All rights reserved. Umbilical cord blood is a recognized source of hematopoietic stem cells for transplantation. It also contains endothelial precursors. In the human, these latter cells not only circulate in the blood prior to birth and postnatally, but are also resident in blood vessel walls of tissues, including the placenta and umbilical cord. It is thought that these endothelial precursors are essential for blood vessel formation and repair in both health and disease and that their dysregulation contributes to serious disease. There has been considerable confusion between these precursors of the endothelial lineage and proangiogenic hematopoietic cells which have been described as circulating "endothelial progenitor cells." Here, we will define cells found in umbilical cord, umbilical cord blood and placenta that generate endothelial cells, distinguish these from proangiogenic cells, assess factors that influence their abundance, and discuss their potential importance in vascular research and as therapeutics.