Polyurethanes offer the greatest versatility in compositions and properties of any family of polymers. For implantable medical devices, a few specific elastomeric polyurethane compositions have demonstrated a combination of toughness, durability, biocompatibility and biostability not achieved by any other available material. Because of the complex behavior of implantable polyurethanes in the body environment, designers and fabricators of polyurethane-containing devices must pay particular attention to the choice of composition and design of components. Subsequent treatment during qualification, fabrication, sterilization, storage, implantation, in vivo operation and explantation also determine the performance and provide the means for assessing the efficacy of the polyurethane in the implanted device.