In this article it is shown that cohabitation (not legally married but living under marriage-like conditions) is an old Nordic tradition still remaining to some extent in Iceland and frequently occurring in Sweden and Denmark. Evidence proves that the ancient tradition of cohabitation is returning. It is assumed that the phenomenon of a post-industrialized society is instrumental in causing the societal change into this renewed social institution of cohabitation. It is also shown that the dyad as a stable unit is still popular, and thus that the nuclear family system is still preferred and prevalent.