Optical aperture synthesis (OAS) may be used to obtain images of much higher resolution than "seeing"-limited observations presently made from the ground. The principles of OAS are essentially those used in radio astronomy and may be applied to space-based or to ground-based observations. The greater spatial resolution obtained would facilitate the imaging of stellar envelopes around Be stars, the study of the internal dynamics of active galaxies, etc. The application of aperture synthesis techniques in space, at visible and at ultra-violet wavelengths, should permit imaging of much fainter sources than would be possible from a terrestrial telescope array. Infra-red observations are best made from the ground. A summary of the conclusion reached by the Space Interferometry Study Team set up by ESA will be presented. A short description of the important parameters relevant to a space mission (attitude control, orbit, structural dynamics, etc) and a comparison to terrestrial atmospheric conditions will be given. Possible instrument configurations will be described and it will be shown that a large field of view may be achieved, so that the instrument may be calibrated on bright stars whilst observing faint sources. Mission concepts for a "monostructure" ~30 metres in size will be examined and a possible strategy for Space Interferometry in the next 20 years considered.