Institutionalized nonmarital sex in an eastern Indonesian society A recent revival of anthropological interest in kinship has evidently extended even as f ar as such long-standing questions as the universality of 'marriage'. More particularly, Cai Hua (2001) has argued that marriage is encountered in all societies except one: the matrilineal Na or Moso of southern China, who ensure biological and social reproduction by way of impermanent sexual liaisons called 'visits'. Continuing in a universalist vein, Cai (2001:426) further claims that marriage and the Na arrangements, whereby a man and a woman meet solely for the purposes of sex, are mutually exclusive; in other words, that an institution of marriage precludes all other forms of institutionalized sexuality. The present essay controverts Cai's thesis in an especially telling way: it explores an eastern Indonesian society in which an approved and institutionalized form of temporary sexual relationship exists (or until recently existed) not only in tandem with marriage, but also with affinal alliance, a system in which marriage and marital sexuality form an essential part of connections between structural groups, and which has usually been conceived as entailing a marriage prescription (Forth 1993:96-7). Insofar as it provides an alternative means of social as well as biological reproduction, the Indonesian institution also bears significantly on continuing theoretical debate in anthropology regarding such analytical categories as descent, filiation, and social kinship. Drawing on accounts of numerous informants I have known during a series of visits to Indonesia over a period of twenty years, in what follows I describe a form of premarital or extramarital sexual relationship among the Nage and Keo of the island of Flores. The relationship involves young unmarried women regularly and openly becoming temporarily attached to men-either married or unmarried-for the purposes of sex. Nage and Keo GREGORY FORTH is Professor and Associate Chair in the Department of Anthropology at the University of Alberta and holds a doctorate from the University of Oxford. Having a special interest in kinship and marriage, religion, symbolism and ethnobiology, he is the author of Beneath the