Commercial aviation relies almost entirely on subsonic fixed wing aircraft to constantly move people and goods from one place to another across the globe. While air travel is an effective means of transportation providing an unmatched combination of speed and range, future subsonic aircraft must improve substantially to meet efficiency and environmental targets.The NASA Fundamental Aeronautics Subsonic Fixed Wing (SFW) Project addresses the comprehensive challenge of enabling revolutionary energy-efficiency improvements in subsonic transport aircraft combined with dramatic reductions in harmful emissions and perceived noise to facilitate sustained growth of the air transportation system. Advanced technologies, and the development of unconventional aircraft systems, offer the potential to achieve these improvements. Multidisciplinary advances are required in aerodynamic efficiency to reduce drag, structural efficiency to reduce aircraft empty weight, and propulsive and thermal efficiency to reduce thrust-specific energy consumption (TSEC) for overall system benefit. Additional advances are required to reduce perceived noise without adversely affecting drag, weight, or TSEC, and to reduce harmful emissions without adversely affecting energy efficiency or noise.The primary focus of the SFW Project is on the “N+3” generation; that is, vehicles that are three generations beyond the current state of the art, N, and requiring mature technology solutions in the 2025-30 timeframe. The project also includes technologies appropriate for the near-term (N+1, 2015) and mid-term (N+2, 2020) timeframes as well, and a cross-cutting emphasis on advanced design and analysis tools. Success in overcoming these technical challenges will result in major changes to engine cycle and airframe configurations that will in turn broaden the technology trade space for a variety of subsonic vehicle sizes ranging from large transports to very light jets. These new capabilities will enable the national vision of significant growth in airspace system throughput in coming decades while reducing overall environmental impact.This paper describes the progress the SFW Project has made toward defining a technology portfolio and relevant metrics in order to address its comprehensive energy efficiency and environmental challenges.