In the near future, NASA, the European Space Agency (ESA), China, and Roscosmos all mount crewed missions to the moon. This will constitute the first time astronauts have walked on the lunar surface since the Apollo era. But unlike the "race to the moon," the goal of these programs is not to get there first and leave only a few experiments and landers behind (i.e., "footprints and flags" missions), but to establish a sustained human presence on the lunar surface. This means creating habitats on the surface and in orbit that can be used by rotating crews.