Three qualities come to mind as seeds for success in civil aircraft engine design over the next two decades—care, optimism and judgement; care to exploit and extend the technology of the high bypass ratio fan engine, optimism to continue to seek apparently unconventional concepts, and judgement to identify the opportunities when each should be applied.

This paper accepts this definition of the engine designer's choice and reviews a range of possible trends, some more likely than others. It is in two parts. The first, entitled ‘Conventional Engines', concentrates on the family of high bypass ratio single stage fan engines which has become established as the preferred design for application to aircraft cruising at high subsonic Mach numbers.