From Sam & Max Wiki
Bad Day on the Moon, the light side is inhabited by a civilization of anthropomorphic rats while the dark side is occupied by intelligent 30ft cockroaches. In Bright Side of the Moon, the Moon seems to be uninhabited except for Hugh Bliss's Prismatology resort, called the Blister of Tranquility, and the accompanying gift shop. The Moon was sold to Canada in Bright Side of the Moon for 100 Canadian dollars in order for Sam and Max to buy Bosco's Earthquake Machine. As a result of this the American flag is replaced with the Canadian flag. Whether the moon was sold back afterwards with the American flag put back into place or still in possession of Canada is not yet known.
The Moon has turned out to have a conveniently breathable atmosphere and is easily visited using the DeSoto.