The dissertation is entitled "Patronage and social mobility in the aristocracies of the Principate". Patronage is defined as a reciprocal exchange relationship between men of unequal social status (municipal patronage is excluded). The work falls into three parts. In the first the language of patronage (patronus, cliens, amicus, beneficium, etc.) is defined; the reciprocity ethic implicit in the language is described; and the spheres of social life in which the patronal ideology was applied by Romans are located. The core of the dissertation is devoted to a description of the patronage networks extending from the emperor through the imperial aristocracy to the provincial aristocracy (in particular, that of North Africa). At each level a description is offered of the economic, social and political goods and services exchanged and the types of people who entered into the patron-client relationships. Further, there is an attempt to show that the fact that Rome remained a patronal society in the Principate has broad implications: the distribution of a variety of offices and honors depended solely on patronage; senators continued to be important patrons distributing their own as well as imperial beneficia to their clients; senators and equites were bound together in a single patronal network; and patronage is perhaps the best explanation for the increasing entry of provincials into the imperial aristocracy. Traditionally it has been argued that the importance of patronage in the Principate was diminished by increasingly rigid bureaucratic machinery in which appointments and promotions were based on merit and especially seniority. Chapter three provides a demonstration that the influence of these bureaucratic criteria on senatorial and equestrian careers have been greatly overestimated and that there is no reason to minimize the effects of patronage.