Combining cross-national surveys with a lab-in-the-field-experiment, this dissertation explores the sources and consequences of socioeconomic segregation in personal networks across three empirical studies. Chapter I provides an overview of the dissertation’s central argument. The first study, a 30-country comparative analysis of the socioeconomic composition of personal networks reveals that individuals’ own socioeconomic position is the primary factor associated with the status and diversity of their ties (Chapter II). Additional analyses show that the magnitude of these relations vary by countries’ characteristics, and that socioeconomic status shapes personal networks in part due to the stratified nature of sociability patterns. Building on the analysis of socioeconomic composition of personal networks and engaging with the current debates surrounding the recent rise in populist politics, the dissertation’s second study argues that socioeconomic segregation is closely related to citizen’s attitudes towards populism (Chapter III). The evidence strongly supports this claim, showing that personal networks not only shape voter preferences for populism but also influence the subjective and attitudinal processes previously associated with populism. The third study, leveraging the Chilean college tuition-waiver policy, uses a lab-in-the-field experiment to manipulate participants’ exposure to contact with peers from different socioeconomic backgrounds (Chapter IV) and finds that cross group interactions increase ingroup prosociality for low-status participants, while decreasing outgroup prosociality for high-status ones. Exploratory conditional effects analyses show that these effects are driven by subjective status perceptions and personal network diversity. Chapter V concludes with a discussion of the dissertation’s findings, limitations, and broader implications.