Angiogenesis, the sprouting of new blood vessels from pre-existing vessels, is a complex, multicellular phenomenon involving capillary endothelial cell (EC) proliferation, migration, and tissue infiltration. The elucidation of the biochemical and molecular factors which control angiogenesis is fundamental to our understanding of normal blood vessel development, as well as of the pathogenesis of abnormal blood vessel formation. Angiogenesis is associated with numerous physiological processes, including embryogenesis, wound healing, organ regeneration, and the female reproductive cycle. However, abnormal angiogenesis also plays a major role in the pathogenesis of tumor growth, rheumatoid arthritis, atherosclerosis and various retinopathies. The cellular and molecular mechanisms underlying both physiological and pathophysiological angiogenesis are only now beginning to be understood. Vascular endothelial growth factor was initially discovered as an unidentified tumor-derived factor which increased microvascular permeability (vascular permeability factor, VPF). Subsequently, it was determined that the protein exhibited mitogenic effects on endothelial cells, but not other cell types. Multiple receptor subtypes have been described which may in part explain the multiplicity of biological actions that have been ascribed to VEGF/VPF in the literature. In this overview, we briefly summarize what is currently known about VEGF and VEGF receptor biology, as well as VEGF receptor signal transduction mechanisms in endothelial cells.