Nowadays most of us assume we will feel sexual desire either for men or for women and that we will be able to tell one from the other. This does not seem to be the case in Gottfried von StraBburg's Tristan und Isold. To be sure, women only desire men and men only desire women. Yet it's hard to see how they can keep themselves straight, since one can scarcely tell the men's bodies from the women's. When bodies are described as desirable, sex-specific features are not mentioned, and when men or women are described as beautiful, they are said to be beautiful in the same terms. And yet, somehow, the inhabitants of Gottfried's fictional world must be able to tell the men from the women, since they will always desire someone of the other sex. What sort of sexual economy ensures that women and men will always desire the other sex when the anatomy of desire scarcely distinguishes one sex from the other? How does heterosexuality work in a homomorphic world?