The principal axiom of materials science asserts that the properties of materials are determined by their structure at various length and time scales. Applying this principle to the process of engineering design has emerged as one of the most challenging problems facing science and engineering in the 21^st century. A functional link is necessary in order to couple the selection and production of materials with specific characteristics to the design of engineering components in a manner that permits material design to become part of a robust design process. Development of physics-based models that relate structure to properties is central to this goal. Models must be not only based on sound physical principles but also cast in mathematical forms that permit them to be inserted in software used for engineering design. The U.S. Air Force is a leader in the sponsorship and conduct of research in this area. Following a discussion of the motivation for this paradigm, the presentation will describe several research projects sponsored by AFOSR that address the issue of integrating materials science and engineering with engineering design. The talk will conclude with a description of recent work by the author on the development of a simple, physics-based model for the composition dependence of single crystal elastic constants of single-phase alloys having lattices in the cubic crystal system.