The superplasticity phenomenon, which is characterized by a metal's capacity for a large degree of relative uniform extension, is reviewed for the purpose of assessing both its potential applicability to practical metallurgical operations and the possible benefits to be derived from further research and development. Detailed are the requirements for a metal to be superplastic, as well as the conditions necessary for the phenomenon to occur. Twenty-nine metal systems reported to be superplastic are listed, including pure metals and singlephase and multi-phase alloys. A number of the methods are reviewed that are employed to generate the required fine grain structure--in the order of a micron- mechanically by extrusion or rolling, or thermally by eutectoid decomposition or compact sintering. It is concluded that superplasticity may be found in many other metal systems that possess a stable micrograin size within the limited temperature and strain-rate range in which a high strain-rate sensitivity can exist. Potential applications of superplastic metals by extruding, rolling, deep forming, coining, bulge-forming, and die-less wire drawing are reported. Possible problems in connection with the use of superplastic metalssuch as oxidation, formation of voids, and strain-rate control--are discussed. Many of the commercial alloys reported to be superplastic will owe their acceptance to their improved mechanical and chemical properties rather than to their remarkable high-temperature ductility. The future application of the superplastic effect is viewed as being most successful when used to form large parts that are beyond the capabilities of most presses.