Introduction to the ``Symposium on Social Networks and Peer Effects: In Memory of

Toni’s numerous contributions to the understanding of social networks and peer effects in economics had quickly made it clear that he was one of the leading economic theorists of his generation. His research was inspired by important instances of social interactions, such as understanding the incentives for individuals to engage in criminal behavior, or how the transmission of information about jobs through social networks affects employment patterns, wages, and education. For example, his paper “Who's Who in Networks: Wanted the Key Player”, with Coralio Ballester and Yves Zenou, provided a new and powerful model of how strategic complementarities among people connected in a network impacts their behaviors including criminal activity levels, and shows how their behavior can be understood through measures of centrality and influence. This model has already become an important building block in the literature, as made clear by the fact that two of the papers in this volume are based on it. Toni made extensive contributions to modeling job contact networks, including an important paper “Job Contact Networks” which provided insight into how the job finding process relates to network structure and how that influences agents’ incentives to form and maintain relationships. His paper “The Effects of Social Networks on Employment and Inequality”, with Matthew Jackson, showed how observations about unemployment patterns and persistent inequality across different groups could be better understood by noting that the spread of job information through social networks leads to systematic correlations in employment of pathconnected individuals, resulting in spatial and time series correlations, and complementarities in education investment decisions. Through these and other contributions Toni’s research made clear that putting economic interactions in a social context could lead to new and important insights about economic decisions and outcomes.