In many, many cases, people have a preference for working and doing business with those who share the same religious beliefs, come from the same geographic region, or have something else in common. If this preference arises from discrimination against other groups – if there is economically inefficient favoritism – the economy will not reach its full potential. But could there also be efficiency gains from transacting with people who are culturally proximate? If so, is it possible for the gains to be large enough to more than offset the losses from discrimination? Surprisingly, the answer to both questions is yes. However, that does not mean the barriers between groups should be reinforced. Policies that break down informational barriers between groups could produce further gains.