Angiogenesis is a complex process involving multiple cell types and growth factors. As putative pro-and anti-angiogenic factors are identified in various model systems, there is a need to validate these factors, and extend their biology, in more complex systems. Transgenic mice have proven a powerful tool for studying the basic mechanisms of angiogenesis and examining the role of angiogenesis in various diseases. In most transgenic approaches, a growth factor or intracellular signaling protein is overexpressed under the control of a cell-or tissue-specific promoter. If expressed in a constitutive system, the factor will not produce an immunologic reaction and can act throughout development. If expressed in an inducible system, the factor can be switched on and act on otherwise normal tissue. This ability—to match the expression pattern of the gene to the experimental question—is crucial to dissecting the actions of angiogenic factors.