At the crossings of economic sociology, work sociology and management tools, this thesis' aim is to clarify the conditions of making durable a niche market of which the existence seems to be a centerpiece for the organization of naval exchanges in globalization. The analysis focuses on a key moment of transportation, a pivot transaction, the shift of goods from the earthly sphere to the naval sphere. While this key moment is traditionally studied within port complexes, our original empirical study emphasizes on a badly-known occupation which is, however, determining in shipping: shipbrokers. These facilitating intermediaries allow, from their offices, the link between two levels of the voyage charter in sea transport: the goods on one hand ...