A recent systems study of the potential for a successful U.S. High Speed Civil Transport (HSCT) has addressed technology, economic and environmental constraints. The study was carried out by Boeing under NASA contract NAS1-18377. Market projections indicated the need for fleets of transports with supersonic cruise speeds by the years 2000 to 2005. The associated design requirements called for a vehicle to carry 250 to 300 passengers over a range of 5,000 to 6,500 nautical miles. Analyses led to a focus on the most promising concepts which cruised at Mach numbers between 2.0 and 2.5. Further systems studies identified the impact of environmental constraints (for engine emissions, community noise and sonic boom) on economic attractiveness and technological needs.Results showed the development of a viable U.S. HSCT early in the 2000's time frame presents a formidable challenge. Economic viability will require a vehicle, when compared to Concorde, that will have three times the payload, approximately twice the range, a tenfold reduction in community noise and allow profitable airline operation with fares reduced by a factor of seven. Current technology is insufficient and the development of a viable HSCT will require aggressive technical advances in many areas to ensure that it is technically feasible, economically viable, and environmentally acceptable. This will require the combined efforts and resources of industry, NASA, academia and other government agencies over a considerable period of time. This paper discusses the key technologies (both enabling and enhancing) that are essential to achieve viability, and the required timing dictated by market projections.