Much empirical evidence shows that female and male partners look alike along a variety of attributes. It is however unclear whether this positive sorting is the result of either assortative or agreed-upon preferences or of meeting opportunities. We assess the nature of dating preferences and the relative importance of preferences and opportunities in dating behavior using unique new data from a large commercial speed dating agency. We find that both women and men value physical attributes, such as age and weight, and that preferences are assortative along age, height, and education. The role of preferences, however, is outplayed by that of opportunities. Along some attributes (such as education, occupation and smoking) opportunities explain more than two-thirds of the estimated variation in demand. Along other attributes (such as age), the role of preferences is more substantial, but never dominant. These results will have important implications for our understanding of the degree of social openness and mobility.