My dissertation investigates the cultural practice and function of collectivities of Roman citizens living outside the Italian peninsula. Using an interdisciplinary analytic framework that accommodates evidence from contexts across the empire, it argues that associations of Roman citizens reshaped local cultural and political structures through the selective adoption of local customs and the establishment of regional trade networks. It also uses social network analysis to demonstrate communication flows between discrete associations of Roman citizens. The data it has collected contributes a new understanding of how colonization occurs through the voluntary acts of private individuals in the absence of state actors. By applying methodological approaches from anthropology and sociology, my project expands current knowledge on the local impact of associations of Roman citizens and emphasizes the diversity of ancient diasporas.