A general method of selection of backfill material for nuclear waste disposal has been derived from a large body of data on sorption of actinides and fission products. These sorption studies identified four major factors of importance in enhancing sorption: (a) pH, (b) chemi-sorption, (c) oxidation-reduction, and (d) special reactions with clay minerals. It appears that simple cation exchange plays a very minor role, especially in the pH range of 7 to 9 that is common to groundwaters. In addition to consideration of radionuclide retardation, physical factors such as water retardation and thermal conductivity have been incorporated in the design. All of the materials employed in the backfill are natural minerals that are commercially available.