Vascular endothelial growth factors (VEGFs) constitute a group of structurally and functionally related growth factors that modulate many important physiological functions of endothelial cells. Currently, five different mammalian VEGFs have been identified and they all show unique temporal and spatial expression patterns, receptor specificity and function. The VEGFs may play pivotal roles in formation of the vascular systems during embryonic development, in regulation of capillary growth in normal and pathological conditions in adults, and in the maintenance of the normal vasculature. In the future, the VEGFs and their receptors may become important therapeutic tools in treatment of conditions characterized by aberrant or defective formation of blood vessels and lymphatic vessels.