Angiogenesis is a critical step in the progression of tumours from dormancy to a clinical relevant cancer. Inhibition of this process is one of the most promising new anti-cancer strategies. To develop new drugs that interfere with the cascade of events required for the formation of new blood vessels, insight into this process is essential. Here, we discuss the molecular basis of angiogenesis and the concepts of vascular targeting. Furthermore new strategies will be discussed to discover surface markers on endothelial cells that confer sufficient specificity for targeted intervention in the tumour vasculature.