Libraries and other collecting institutions should keep up to date on the stability characteristics of available color print and film materials, both to select the most stable products for in- house use and to be able to offer advice to others about which products will best meet their needs. Polaroid Permanent-Color prints are the best color prints that can be considered to be truly permanent, both when exposed to light during prolonged display and when stored in the dark. Permanent-Color prints, which can be made from color negatives, transparencies, or existing color prints, have images formed with special, highly stable color pigments instead of the dyes used in other types of color photographs. Making the prints is a fairly complex procedure that is best handled by specialized processing labs. The classification of ultra-stable was proposed to describe the stability characteristics of the then-new Polaroid ArchivalColor process (later renamed the Polaroid Permanent-Color process) and to differentiate this extraordinary level of stability from the less stable ANSI archival classification that is applied to acetate or polyester-base silver gelatin films. Materials included in the proposed ultra-stable group were black-and-white photographs on polyester-base film or fiber-base paper with toned silver gelatin images (light and dark storage); Polaroid Permanent-Color prints (light and dark storage); Ilford Cibachrome, Kodak Dye Transfer, and Fuji Dyecolor (dark storage only). Black-and-white RC prints, acetate-base films, and polyester-base films or fiber-base papers with untoned silver images were excluded from the ultra-stable classification. Although subject to light fading, Ilford Cibachrome polyester-base prints and color microfilm also can be considered permanent when kept in the dark; this property makes Cibachrome unique among conventional (simple to process) color materials. Under commonly encountered dark-storage conditions, Cibachrome polyester-base materials should last far longer than most black-and-white photographs.