Owing to the increasing use of cryogenic propellants such as liquid oxygen and liquid hydrogen in missiles and space vehicles, the properties of high-strength structural materials at extremely low temperatures are becoming of prime importance to the national aerospace program. The papers in this symposium consider the mechanical properties of promising high-strength structural alloys at temperatures ranging down to −423 F. Papers pertaining to aluminum, magnesium, titanium, and stainless steel alloys are presented which treat most of the high-strength structural materials used at low temperatures in current and proposed missiles and space vehicles. The alloys reported upon were generally selected for study because they exhibited one or more of the following characteristics which suited them for missile and space vehicle application: high strength to density ratios; good toughness (that is, resistance to brittle fracture); adequate weldability; corrosion resistance; and good formability. In order to obtain optimum strength levels, the particular alloys selected for study were either cold worked (that is, cold rolled) or heat treated (for example, age hardened, or quenched and tempered) to their highest strength levels commensurate with adequate toughness. Since this symposium is aimed primarily at missile and space vehicle applications, attention was focused on sheet alloys since large cryogenic propellant tanks are fabricated from thin-gage sheet. In addition, since weldability is of prime importance for the pressure integrity of these tanks, the sheet alloys were reported upon in both the base metal and welded joint configurations whenever possible.