Astronomical instrumentation has improved steadily with time as technological progress has allowed the demands of astronomers to be satisfied. There can be little doubt that astronomers will continue to seek improved performance but in some respects the performance achieved is already close to physical limits while in others technology or available funding are the limiting factors. Resolution has always been important to astronomers, not only because of the additional structural detail that improved resolution may reveal but also because of the improvement in ability to detect and study faint unresolved objects in the presence of background radiation. The purpose of this paper is to review the resolution currently obtainable at wavelengths shorter than 100 μm and to examine the extent to which improved resolution could be obtained with only modest extensions of current technology. The review is confined to consideration of telescope resolution and does not include the performance of detectors.