Following the “refugee crisis,” Germany has faced a rise in both right-wing and Islamist extremism. It has been argued that sports contexts may be suitable to reduce intergroup tensions including its more extreme forms, yet empirical research backing this claim is scarce. Against this background, this study explored how ethnic diversity of teams and intergroup perceptions of its players independently and interactively may be associated with support for violent extremism and threat perceptions. Specifically, it asked: Can extremism and threat perceptions of soccer players be explained by (a) the ethnic diversity within soccer teams, (b) intergroup perceptions and contact experiences of individual soccer players, and (c) cross-level interactions between both sets of factors? To do so, data of 281 players from 60 soccer teams across the ethnically diverse region of North-Rhine-Westphalia, Germany, was analysed using multilevel modelling. Individual intergroup attitudes (social team capital, perceived diversity ideologies, and intergroup contact experiences) functioned as level-1 variables, whereas different measures of ethnic diversity of the teams functioned as level-2 variables. Whereas ethnic diversity within teams alone did not predict the dependent variables, cross-level effects were found. High ethnic diversity predicted less support for violent extremism when the quality of intergroup contact was high, yet more support for extremism when perceived outgroup contact was frequent. Furthermore, when ethnic team diversity was high, players showed more support for violent extremism if they perceived their team to endorse a colour-blind ideology and less support if team colour-blindness was perceived to be low. Limitations and societal implications for the prevention of violent extremism through sports teams are discussed. Please not that this thesis, entitled “Investigating Ethnic Diversity, Threat Perceptions and Extremism in Soccer Teams: A Multi-Level Study” was conducted by Ann-Cathrin Coenen under the supervision of Dr. Jonas R. Kunst at the Department of Psychology at the University of Oslo as part of the requirements for the joint master’s degree in the Psychology of Global MINDS (Mobility, Social Inclusion, and Diversity in Society) in the spring semester of 2019.