Vascular endothelial cells (EC) are derived from hemangioblasts which also serve as progenitors for the hematopoietic cell lineage. Distinct stages of EC development can be described by the expression of characteristic cell markers. During differentiation, EC modulate their expression of multiple cell surface receptors which trigger maturation responses. These receptors also regulate vessel branching and guidance during arteriogenesis, angiogenesis, and lymphangiogenesis. They respond to multiple secreted or cell surface molecules including Angiopoietins, Erythropoietin, Delta, Jagged, Leptin, Sphingosine-1-Phosphate (S1P), SCF, and Serrate.