Abstract: This paper discusses the question of similarity between husband and wife (or, more generally, between the partners of a long-term relationship) from the point of view of economics. Four different economic approaches are presented: Becker's economics of the family, the theory of exchange, the theory of subjective expected utility and transaction cost economics. It is found that, in general, a considerable degree of similarity is to be expected (especially with regard to education, social status and potential income).