The technology requirements for new subsonic transport engines which might go into service in the mid 80's are discussed with the emphasis placed upon improving energy consumption and aircraft economics. A typical advanced turbofan engine is described. Effects of variations in major cycle parameters on fuel usage and direct operating cost (DOC) of advanced aircraft designed for 0.8 Mach no. are shown. The impact of specific engine design and technology features including component aerodynamic and mechanical improvements, high temperature materials and cooling, composites, and advanced nacelle designs is also shown and related to the technology advances required.