In this landmark work of economic sociology, Lucien Karpik introduces the theory and practical tools needed to analyze markets for singularities. Singularities are goods and services that cannot be studied by standard methods because they are multidimensional, incommensurable, and of uncertain quality. Examples include movies, novels, music, artwork, fine wine, lawyers, and doctors. Valuing the Unique provides a theoretical framework to explain this important class of products and markets that for so long have eluded neoclassical economics. With this innovative theory--called the economics of singularities--Karpik shows that, because of the uncertainty and the highly subjective valuation of singularities, these markets are necessarily equipped with what he calls judgment devices--such as labels, brands, guides, critics, and rankings--which provide consumers with the credible knowledge needed to make reasonable choices. He explains why these markets are characterized by the primacy of competition by qualities over competition by prices, and he identifies the conditions under which singularities are constructed or are in danger of losing their uniqueness. After demonstrating how combinations of the numerous and multiform judgment devices can be used to identify different market models, Karpik applies his analytical tools to the functioning of a large number of actual markets, including fine wines, movies, luxury goods, pop music, and legal services.