The phenomenon of illegal markets is pervasive. The circulation of illegal goods and services reaches all social segments, crosses national boundaries, and produces enormous revenues. Scholarship has typically addressed issues of illegal exchanges by focusing on criminal organizations, their members’ activities, internal structures, and businesses while leaving the very notion of illegal markets conceptually underdeveloped. Different from organized crime, the notion of “illegal market” compels us to consider the demand side and to investigate the varied ways it relates to the supply side. Following the path opened up by economic sociology scholarship, this article brings illegal markets to the center of the scene in order to develop them conceptually, observe them in a differentiated way, and investigate their relationships with legal structures. From this perspective, the social organization of markets comes to the fore, highlighting such aspects as the formal and informal institutions sustaining illegal markets; the modes of internal coordination that deal with problems such as value, competition, or trust; moral attitudes toward the production, exchange, or consumption of certain products or services; the cultural elements or cognitive dispositions that promote illegal exchanges; the role of state power in defining what is and is not illegal, and thus how it controls certain exchanges; and the role of the enforcement of the law in the emergence, expansion, or extinction of these markets.