This study of a major group of merchants who helped to build up London's wealth and political influence during the Middle Ages throws new light on the history of the City. This pioneering work is the first major study to illuminate London's mercantile economy throughout the whole of the Middle Ages. It traces its development against a background of plague, foreign competition, war, the Peasants' Revolt, and shortages of coin. It also reveals how a mercantile company functioned, how it affected its members' lives, and what part it played in the social control of the City.