The effects of high-energy irradiation on the structure, properties, and processing of polymers are of considerable scientific and commercial significance and have been reported in several books and review articles [101]. In this massive literature, two of the major radiation-induced changes reported are crosslinking and degradation, sometimes leading to a loss of crystallinity. In fact, in this literature polymers are generally classified as either “crosslinking type” or “chain-scission type.” In the present review we shall not be concerned with radiation-induced crosslinking, although its existence in many polymers is, of course, acknowledged. Nor will our review cover radiation-induced polymerization or grafting. All these topics have already been adequately covered in the extensive radiation literature, such as the references cited above.