Both proscriptions and prescriptions define boundaries between groups. While Lévi-Strauss himself has devoted his attention to those societies where marriage exchanges are structured entirely with reference to descent groups defined genealogically, the principles of marriage exchange also have relevance for an understanding of ethnic group relations. In specific, marriage proscriptions may serve to demarcate the boundaries between ethnic groups. Among the Karen, who live in Burma and western Thailand, for example, strong pressures are brought to bear on those who would transgress cultural expectations and marry non-Karen (see Kunstadter, in press; and Marlowe, in press). Regulation of marriage exchanges does not universally serve to structure relationships (or, more precisely, nonrelationships) between ethnic groups, but the potential always exists and is not rarely made use of.