Epoxies are utilized by the aerospace industry primarily in the form of matrices for composite materials and as adhesives. The increasing use of epoxies requires a knowledge of their lifetimes in extreme service environments. When epoxy adhesives and composites are utilized in primary structural components of airframes, it is vital that the durability of such components be known during design development. A number of laboratory and field studies have indicated that the combined effects of sorbed moisture and thermal environment can cause significant changes in the mechanical response of these materials [1, 2]. However, the long-term, in-service durability of epoxy adhesives and composites in primary structural airframe components is unknown primarily because (1) long-term, in-service aging characteristics are difficult to simulate by short-term laboratory and/or field tests, and (2) the basic phenomena responsible for the changes in the mechanical response in laboratory-simulated service environments have not been identified and/or understood.