In this paper the subject is considered from an aerodynamic point of view and no discussion of the possibilities of structural integration of the engine and airframe in the sense of using parts of the engine to contribute to the structural strength or stiffness of the airframe is included, beyond the statement that the simplest consideration and roughest calculations suggest that the sort of deflections obtained on typical aircraft structures at full load do not seem compatible with the integration into such a structure of engines having rotating parts and fine clearances, although in the case of units such as ram-jets such structural integration may well be practicable and desirable. Another structural problem which leads naturally to the consideration of engine and airframe as a single unit is the problem of improving flutter characteristics by placing the concentrated masses of the engines in suitable positions relative to the wing.