This article is a discussion of the historical development of Al-Zn-Mg-Cu alloys for use in aircraft since the 1930s. High strength has not been the only consideration, as the earliest alloys were as strong as those of today. Rather, the main reason for development of new materials was that early alloys were not adequately resistant to stress-corrosion cracking (SCC). In general, the history of alloy development has involved a tradeoff between strength and tolerance for environmental, geometric, and manufacturing factors, fatigue or other damage in service. Emerging military needs spurred development in the late 1930s. One alloy, 7076, developed in 1940 for use in propeller blades, is still in use today. A range of reliable materials is currently available for use by the aircraft industry. This article may be of interest to conservators working with 20th century aircraft parts.