This memorandum describes the fusion-welding characteristics, mechanical properties, and stress-corrosion behavior of high-strength, weldable aluminum alloys. These are defined as alloys in which sound welds can be produced and in which at least 50 and 70 percent of the maximum base-metal strength can be retained in the as-welded and post-weld-treated conditions, respectively. Careful selection of joining method and filler metals as well as close control of joining-process parameters is necessary to produce high-strength aluminum weldments. Highest strengths and weld-joint efficiencies in high-strength weldable alloys are achieved with the use of postweld aging and/or mechanical treatments. The best combination of highest strengths and good welding characteristics is found in the 2000 and 7000 alloy series. As compared with the 2000 and 5000 alloy series, the 7000 alloy as a class suffer three major property disadvantages: (1) their tendency to be notch sensitive, (2) their tendency to exhibit low toughness at low temperatures, and (3) their much greater susceptibility to stress-corrosion cracking. Nonetheless, several relatively new 7000 series alloys have been developed which show reasonably good notch toughness to -423 F and which are considered competitive with the 2219 and 2014 alloys for cryogenic applications. (Author).