Vascular Endothelial Growth Factor (VEGF) is the most potent and ubiquitous vascular growth factor known to date. Yet, prior to its description as a secreted mitogen for endothelial cells, it was identified as a vascular permeability factor. These seemingly disparate avenues of discovery highlight VEGF's ability to control many distinct aspects of endothelial cell behaviour, including proliferation, migration, specialisation and survival. The versatility of VEGF as a patterning molecule is likely linked to its association with various signalling receptor complexes, but also its expression in several isoforms with a differential affinity for heparan sulfate proteoglycans in the extracellular matrix. In contrast to the absolute requirement for all known VEGF receptors, the presence of only a single VEGF isoform is sufficient for vascular development. However, the isoforms serve as exquisite tools for the fine patterning of growing vessel networks during embryogenesis and in postnatal life. BioEssays 25:1052–1060, 2003. © 2003 Wiley Periodicals, Inc.