Straight Dope Staff Report: Do Eskimo men lend their wives to strangers?:
It's true Eskimo men sometimes let other men sleep with their wives. But did they offer that privilege to any horny schmuck who showed up on the front stoop? Generally not. The lending of wives to perfect strangers happened occasionally in some places, but it was never the widespread custom it has been made out to be.
There were several contexts in which a husband would let another man sleep with his wife. The most widespread was ritual spouse exchange, practiced in one form or another in every region where Eskimos lived, from eastern Greenland to the Bering Sea. This sort of spouse exchange was always associated with a religious purpose, and was always done at the instigation of an angekok (shaman). Often the point was to effect some desired outcome, such as better weather or hunting conditions.
The best known example of ritual spouse exchange was the "putting-out-of-the-lamps game" played in Greenland. This was a sort of combination of seven minutes in heaven, Roman orgy, and prayer meeting. The prayer-meeting aspect failed to overcome the objections of the early Christian missionaries, one of whom called it the "whore game." Those guys really know how to ruin a party. To play at home: gather together a number of married couples (according to some sources, singles could play too); wait for the angekok to contact the spirits; turn out the lights; screw a random member of the opposite sex; turn on the lights. The idea seemed to be that the spirits would be more willing to cooperate if you did it that way. Who are we to disappoint the spirits? This game was played only in Greenland, but other spouse-exchange rituals were practiced elsewhere. One example from Alaska was called the "bladder feast," which sounds a bit less appetizing. (Despite the name, the bladders weren't eaten, and sex was only a minor part of the festivities).