This chapter examines the geologic and engineering dimensions of nuclear waste storage. The waste characteristics, existing and projected quantities of radioactive materials that need to be stored, various disposal or storage strategies or alternatives, geologic media under consideration, and repository construction techniques and problems are discussed. The subject has been exhaustively studied for over twenty-five years. In 1957, a committee of the Division of Earth Sciences of the National Academy of Sciences-Natural Research Council published a report, entitled The Disposal of Radioactive Hastes on Land (National Academy of Sciences, 1957). Since then, research results have accumulated rapidly. The authors of this chapter have between them more than twenty feet of bookshelves of various studies made since 1957, all devoted to this subject, and that is certainly not a complete record. Perhaps the most complete recent summary is the Final Environmental Impact Statement, Management of Commercially Generated Radioactive Waste (U.S. Department of Energy, 1980a). Much of this chapter is summarized from that report. We will concentrate our discussion on commercially generated radioactive wastes because national defense program wastes are managed as a separate program. The characteristics of these Defense Department generated radioactive materials are somewhat different from the commercial wastes; however, in a generic sense, the defense wastes pose similar hazards, and they will probably be stored and managed similarly to the commercial wastes. The discussion presented can thus be seen as generally applicable to the overall nuclear waste storage problem.