[영문]Consider a heterogeneous agent matching model in which the payoff of each matched individual is a fixed function of both partners’ types. In a 1973 article, Becker showed that assortative matching arises in a frictionless setting simply if everyone prefers higher partners. This paper shows that if finding partners requires time-consuming search and individuals are impatient, then productive interaction matters. Matching is positively assortative?higher types match with higher sets of types?when the proportionate gains from having better partners rise in one’s type. With multiplicatively separable payoffs, these proportionate gains are constant in one’s type, and “block segregation” arises, a common finding of the literature.