Focusing of a monochromatic ocean wave image by either a regular or an interferomeric SAR (INSAR) is studied. The model developed simulates the images of both SAR and INSAR for an arbitrary focus setting. The effects of the various operational parameters, i.e., integration and scene coherence times, ocean wave length, direction and amplitude, etc., on the focus sensitivity of both SAR and INSAR is examined. A dimensionless focusing parameter a which depends on the platform velocity and on the azimuthal component of. the phase velocity of the imaged ocean wave is introduced. It is shown that a is the major parameter which determines the image contrast of the regular SAR output, as well as that of the magnitude and the phase components of INSAR. The focus sensitivity, however, is also a function of the imaged ocean wave parameters. The effects of the varying SAR integration time and of the scene coherence time on the contrast of the resulting image is also examined.