Vascular endothelial growth factor (VEGF) is a mitogen and survival factor for endothelial cells and an inducer of angiogenesis and vascular permeability. It is essential for developmental angiogenesis and loss of a single VEGF allele results in early embryonic lethality. VEGF-mediated angiogenesis is also required for female reproductive functions and endochondral bone formation. Substantial evidence also implicates VEGF in tumors and intra-ocular neovascular syndromes. Several strategies are being employed to inhibit VEGF function as a means to treat cancer and age-related macular degeneration. A humanized anti-VEGF monoclonal antibody is presently in phase III clinical trials as a treatment for solid tumors.