Shape-memory polymers (SMPs) are an emerging class of mechanically active materials that are able to change shape or apply forces in response to a stimulus. There are a wide variety of chemistries for SMPs; however, this chapter focuses on the three SMP types that have undergone the most development for biomedical applications: amorphous cross-linked methacrylates, semicrystalline degradable cross-linked methacrylates, and polyurethanes. The mechanical properties (modulus, failure strain, shape recovery, shape fixity, recovery stress) of the SMP materials are discussed along with the performance of their associated clinical and preclinical devices. A number of biomedical applications are in development, particularly in the areas of orthopedic and cardiovascular devices. Possible future biomedical applications of SMPs are also presented.