The Moon offers for astronomy a truly impressive array of advantages, many of which are briefly reviewed in this paper. These advantages include especially the vast inertial platform and the expected availability of human and robotic “hands-on” installation, maintenance, and modification. The Earth-orbiting Great Observatories will advance our knowledge to a new plateau, but some of the most fundamental observational questions which we are already asking will require lunar-based instruments, including very large filled-aperture telescopes, interferometers with baselines of tens and ultimately hundreds of kilometers, and the utilization of the radio-quiet backside. It is already time to begin planning the first such installations.