Examination has been made in some detail of air transportation demand trends, air transportation system goals, and air transportation system trends well into Century 21. The outlook is for continued growth in both air passenger travel and airfreight movements. The present system, with some improvements, is expected to continue to the turn of the century and to utilize technologically upgraded, derivative versions of today's aircraft, plus possibly some new aircraft for supersonic long haul, short haul and high density commuter service. Severe constraints of the system, expected by early in Century 21, should lead to innovations at the airport, away from the airport, and in the air; and innovations are illustrated by descriptions of three candidate systems involving advanced aircraft concepts. Advanced technologies and vehicles expected to impact the airport are illustrated by descriptions of laminar flow control aircraft, very large airfreighters and cryogenically fueled transports.