Endothelial cell activation and dysfunction underlie many vascular disorders, including atherosclerosis, tumor growth, and sepsis. Endothelial cell activation, in turn, is mediated primarily at the level of gene transcription. Here, we show that in response to several activation agonists, including vascular endothelial growth factor (VEGF), tumor necrosis factor-α, and thrombin, endothelial cells demonstrate rapid and profound induction of the early growth response (Egr) genes egr-1 and egr-3. In VEGF-treated endothelial cells, induction of Egr-3 was far greater and more prolonged compared with Egr-1. VEGF-mediated stimulation of Egr-3 involved the inducible binding of NFATc, serum response factor, and CREB to their respective consensus motifs in the upstream promoter region of Egr-3. Knockdown of Egr-3 markedly impaired VEGF-mediated proliferation, migration, and tube formation of endothelial cells and blocked VEGF-induced monocyte adhesion. Egr-3 knockdown abrogated VEGF-mediated vascular outgrowth from ex vivo aortic rings and attenuated Matrigel plug vascularization and melanoma tumor growth in vivo. Together, these findings suggest that Egr-3 is a critical determinant of VEGF signaling in activated endothelial cells. Thus, Egr-3 represents a potential therapeutic target in VEGF-mediated vasculopathic diseases.