Referring to the “promise” of something is likely to imply that little has been accomplished. This is not true in the present case however. In optical interferometry, for example, there has been a steady development during the last decade or so after somewhat of a lapse subsequent to Michelson and Pease’s work some 65 years ago. Most of the work to date, however, has been directed towards the measurement of stellar diameters and binary stars and is hence not germane to the present topic of reference frames. What is required for the latter is the analog of the phase coherent interferometers used with such conspicuous success in radio interferometry. The important point is that such analogs are now available in both the optical and infrared (10u) wavelength regions.