Abstract: Disclosed are occluders and methods of their use. The occluders comprise shape-memory polymeric materials which, when heated above their crystalline melting temperatures, may be deformed from a first configuration into a second configuration. The occluder is then held in the deformed shape until it cools to a temperature below its crystalline melting temperature (Tm) whereby it holds the deformed shape of the second configuration by virtue of the recrystallization of the polymeric occluder material. Upon reheating the occluder above its Tm, the occluder will resume its original shape. In this manner, an occluder which has been deformed to reduce its diameter may be inserted into and positioned within a target lumen in the body and then allowed to warm to body temperature whereby it resumes its original diameter and results in the occlusion of the lumen. The occluders, according to preferred embodiments, may be used for reversible sterilization of mammals, among other surgical and non-surgical uses.