A comparison of opportunities for optical aperture synthesis from the ground and from the moon suggests that the lunar surface (at night) will be an excellent site for interferometry to faint limits in the intermediate wavelengths, 4–20 &mgr;m. At shorter wavelengths, ground‐based observations are competitive. In the 5–20 &mgr;m region, ground‐based will be competitive if the background photon limit can be reached. Baselines up to 3 km will be required. In the far infrared, ≳40 &mgr;m, the faintest IRAS sources could be measured, and many of the brighter sources imaged, with baselines up to 0.6 km. The temperature of the lunar environment limits the likely far infrared performance of a lunar based system. The cooler ambient temperatures in the polar regions do not offer substantial sensitivity gains.