The blanket is one of the largest and most complex systems in a fusion power reactor. In a D-T fueled reactor the blanket system recovers the energy produced by the fusion reaction and provides for breeding and recovery of tritium for the fuel cycle. The blanket must operate in a severe neutron-radiation, thermal, chemical, mechanical, and electromagnetic environment. Consideration of the required functions of the blanket and the general chemical, mechanical, and physical properties of candidate tritium breeding materials, coolants, structural materials, and so forth, leads to acceptable or compatible combinations of materials. The presently favored candidate structural materials are the austenitic stainless steels, martensitic steels, and vanadium alloys. The characteristics of these alloy systems which limit their application and potential performance, as well as approaches to alloy development aimed at improving performance (temperature capability and lifetime), will be described. Progress toward understanding and improving the performance of structural materials has been substantial. It is possible to develop materials with acceptable properties for fusion applications.