In the author's R. J. Mitchell Memorial Lecture, presented to the Southampton Branch of the Royal Aeronautical Society in March 1969, the role of aircraft in future transport systems was examined. Since that time, three important trends or events have taken place. First and probably the most important, the environmental problems arising from the use of aircraft—noise, pollution and land use—have come to be major parameters in the design of new airliners. This trend has been highlighted by the recent issue of noise regulations by the Federal Aviation Administration (FAA) which new airliners have to meet before they can be certificated. These limits can be expected to become more stringent in future years. Secondly, the economic effects of congestion—both in the air and on the ground, at and around airports—have begun to be felt at major airports, especially at those in the Northeast Corridor of the United States. Finally, in the United Kingdom the Roskill Commission on the Third London Airport has recently issued its report.