The leading question behind this dissertation is: how did trade operate in the Roman Empire under conditions of imperfect government enforcement in private contracting, and of imperfect information? The Roman State, unlike modern states, did not employ the powers at its disposal to enforce private contracts made under the rules of its legal system. Given the lack of government support, information on merchants' reliability and trustworthiness was extremely important in conducting long-distance trade. However, under pre-industrial conditions information could only travel slowly, making it difficult for merchants to assess risk. This dissertation offers a micro-economic model of how these problems were solved in the Roman Empire. It argues that information circulated within networks defined by geographical origin, with the loss of one's reputation or trading position within those networks forming the instrument of enforcement. The discussion consists of three main parts: intra-community trade in the Italian harbor-city of Puteoli; inter-community trade between the provinces and Puteoli, Ostia, and Rome; and finally inter-community trade between Italian merchants and the provinces