Actual and potential composite applications in commercial and military aircraft gas turbine engines range from low temperature graphite/polymer matrix composite (PMC) components at the front of the engine, such as, fan blades, vanes, struts and cases, to high temperature ceramic matrix composite (CMC) turbine, combustor, augmentor, and nozzle components. Currently the “building block” approach is primarily used in the development of composite components for gas turbine engines. Critical issues associated with the design of composite structures for both commercial and military aircraft gas turbine engines are defined. Critical structural components for both commercial and military gas turbine engines are designed to meet strict safety-of-flight requirements established by the FAA and the Air Force/Navy, respectively. Key design requirements established for damage tolerance and durability are emphasized.