Protocols outlined in this chapter illustrate how to prepare and analyze angiogenic cultures of rat aorta. Aortic rings embedded in gels of extracellular matrix generate vascular outgrowths that can easily be monitored over time with inverted microscopy. The angiogenic response can be measured by counting vessels or with image analysis. Aortic ring cultures can be used to investigate molecular mechanisms of angiogenesis and test the efficacy of stimulators and inhibitors of the angiogenic process. As such this assay is an invaluable tool for both basic and applied angiogenesis research.