The term prostitution is often used as a metaphor for qualifying immoral economic conduct. Yet references to this metaphor in the history of economic thought reveal that more than ethics is at stake. Prostitution sometimes designates a unique economy, different from the basic tenets of orthodox economics. It is an economy where money is an obscene object, disrupting the very possibility of equivalence on which orthodox economics is based. This peculiar conceptualization of money is essential for understanding the historical specificity of capitalism. Applying it to the recurring cultural association between finance and prostitution, this essay unearths the gendered aspect of capitalism. In capitalism gender relations are formally excluded from the sphere of exchange. The traditional notion of marriage as a purchase of a wife has become obscene, but its obscenity attests that its exclusion is indeed formal and that it continues to inform economic practices and imagination.