Due to a trend towards very high-bypass ratio engines and a corresponding close coupling of engine and airframe, the minimization of adverse interference effects is an important aspect in aircraft design. Investigations of engine/airframe integration have been carried out within a long-term collaborative European research initiative, starting in 1990 with the programs DUPRIN I, DUPRIN II to the current ENIFAIR and AIRDATA projects. Based on some selected results the contribution highlights major outcomes of the numerical activities accompanying the experimental studies in the aforementioned programs. After a brief introduction to the basic aerodynamic phenomena of engine/airframe interference and the numerical methods in use, the capabilities of the theoretical approach are demonstrated for three aspects: The influence of increasing engine size on the aerodynamic interference is outlined by simulating turbine powered engine simulators (TPS) of different bypass ratio on the ALVAST narrow body wing/fuselage model. Second, the influence of position variations is demonstrated for different engine concepts, representing the major design parameter for influencing engine/airframe interference. Finally, the jet influence is stressed by comparing numerical results for different thrust conditions. The investigations show, that the lift loss, caused by the mounting of engines, is proportional to the engine size. An upstream movement of the engine position alleviates the lift loss, whereas a vertical movement does not have a significant influence. Especially for the VHBR and UHBR concepts the incorporation of the engine jet is essential to assess the aerodynamic interference. In general validated numerical methods are capable to simulate the dominant features of engine/airframe integration. [Copyright &y& Elsevier]