What Extreme hostility is entering political debates, especially on social media. Professional politicians have become frequent targets of online threats and citizens find online discussion dominated by extremist viewpoints. Democratic societies are thus facing a new challenge: Frequent and intense online political hostility. The Center for Research on Online Political Hostility (ROPH) will meet this challenge by identifying the (1) causes, (2) consequences and (3) counter-strategies related to online political hostility. In essence, ROPH will answer questions like: Why do offline political frustrations escalate into genuine hostility when discussions go online; what are the consequences for victims and democracy alike; and how can online political hostility be stopped? Why Online political hostility is a unique occurrence of mass extreme behavior within democracies. It adds fuel to the fire in societies already facing tensions over rising political polarization and deepening social inequality. Furthermore, its frequency suggests that it emerges in individuals far beyond traditional extremists. As more and more political discussions occur online, it is therefore crucial to develop tools that can decrease online hostility. Policy solutions that remedy frustrations related to polarization and inequality will be difficult, if not impossible, to sustain and legitimize without civilizing online discussions. How To pinpoint the causes and consequences of online hostility, ROPH is developing a new data approach optimally geared towards analyzing the spillover dynamics between offline and online contexts. In essence, ROPH advances a shift from ‘big data’ to ‘integrated data’. To understand online political hostility, we need data on what people bring with them from their offline context in terms of psychological, sociological and political predispositions. And we need data on what people take away from the online context in terms of perceptions of themselves, others and democracy at large. That is, ROPH will integrate social media data (analyzed with the tools of ‘big data’ analysis) with attitudinal, behavioral and register-based data obtained outside of social media platforms. SSR A key goal of ROPH is to provide proof-of-concept for a range of interventions that can prevent, interdict and mitigate online political hostility. On the basis of insights about causes and consequences, ROPH will develop interventions and test their effectiveness in reducing online political hostility combining randomized experiments and social media data. The goal is to establish a set of interventions for helping citizens manage their online emotions, which are directly implementable by educational institutions and the tech industry. To achieve this, ROPH is working together with key private and public actors to validate the proposed interventions and disseminate them.