Vasculogenesis, the generation of new blood vessels de novo, and angiogenesis, the formation of new blood vessels from preexisting vessels, are mediated by a number of cytokines and growth factors among which vascular permeability factor/vascular endothelial growth factor (VPF/VEGF) is one of the most important. VPF/VEGF is secreted by many tumor cells, at sites of wound healing and chronic inflammation, and in physiological angiogenesis as in corpus luteum formation. VPF/VEGF is a multifunctional cytokine that interacts with two high affinity tyrosine kinase receptors that are selectively expressed on vascular endothelium. This interaction triggers an angiogenic cascade whose steps, among others, include increased microvascular permeability, leading to deposition of a pro-angiogenic extracellular fibrin matrix, and the formation of mother/daughter vessels.