I am a Professor of Sociology at the Institute of Sociology and Social Psychology at the University of Cologne. My areas of interest are action theory and social networks, diversity and social boundaries, and crime and deviance. Recent publications include an annual review piece on analytic criminology (with Per-Olof H. Wikström) and several studies on social networks and identities in adolescence, based on theERC project SOCIALBOND. At Nuffield, I will continue my work on ethnic diversity in the school context and finalize a manuscript on the role of friendships for helping Jews during WWII (with Miles Hewstone).