The Apollo missions established the Moon as a cornerstone in planetary science: insights gained from this coign of vantage have stimulated research and influenced ideas for the Earth and other planets subsequently investigated using spacecraft. The history of lunar studies emphatically demonstrates the enormous progress in knowledge and understanding—a giant leap—that is made when samples from another planet become available for study in sophisticated laboratories. A few pebbles kicked loose are enough to start an avalanche, and the lunar samples are used as test beds for hypotheses about planetary, and even solar, evolution. The Moon is more accessible than any other body in the Solar System and is a potential home for a permanently occupied base with multiple purposes; it remains an important target for future work in planetary science.