Excellent physical properties and blood compatibility characteristics have made polyurethanes a promising biomaterial for the manufacture of vascular grafts, especially those of 6 mm ID or less. In this chapter, published and patented methods for graft manufacture and testing are reviewed briefly. In addition, methods developed by the authors are described in detail. Results of experiments on the ability to control graft characteristics by altering the fabrication process are also presented. Some in vivo results of these grafts are also discussed with respect to the identification of principal failure modes.