If laid end to end, the vessels from a typical adult would circle the Earth twice. Little surprise then, that the process of growing new blood vessels - angiogenesis - is a fundamental biological mechanism that can result in serious disease when it goes wrong. More than US$4billion has been invested in the research and development of new drugs to promote or inhibit angiogenesis, making it one of the most heavily funded areas of medical research today. This Nature Insight describes many of the physiological processes and introduces exciting applications that have recently been made available.
