Kip V. Hodges Harrison H. Schmitt July marked the beginning of a 3-year-long celebration of one of the most remarkable periods of human exploration in history: the Apollo missions to the Moon. Reflections on Apollo have inspired a renewed international interest in sustained lunar exploration. While there are many motivations for traveling to the surface of the Moon, experience shows that a sustained program of science activities on the lunar surface would yield unique and invaluable scientific data. Although the Apollo missions themselves ended nearly five decades ago, Apollo science continues today. Building on field scientific observations and sampling by the Apollo astronauts, we now know that the Moon is very old, forming perhaps only a few tens of million years after the 4.56-billion-year origin of Earth and the Solar System. Unfortunately, our planet preserves only sparse evidence of its own ancient history as a consequence of the continuous recycling of Earth’s crust through plate tectonics. There are no plate tectonics on the Moon and none of the erosional effects of wind, water, and flowing ice that drive most of the surface evolution of Earth. As a consequence, the Moon represents an …