A 3-meter two telescope stellar interferometer has been used to observe fringes for the past year in order to study the feasibility of using long baseline interferometers for astrometry. We have demonstrated that two color fringe measurements are capable of significantly reducing the astrometric error due to atmospheric turbulence. Currently, we are investigating the thermal and mechanical sources of error in the instrument. The results of our study will be incorporated into the design of the 20 meter astrometric interferometer which will be built in the next 1–2 years. The key to the 20-meter interferometer is the laser system which we expect to monitor all the mechanical and thermal imperfections relevant to astrometry at the 10−3 to 10−4 arc sec level. A slight modification of this system could be used in a space based interferometer for 1 to 10 microarcsecond astrometry of faint objects.