Social media have democratized the public expression of opinions not only for those who debate constructively but also for those who vent their anger and attack and silence others. In recent years, aggressive online commenting in social media has become highly visible, common, and socially relevant. Politicians are threatened on Facebook, organizations are showered in collective outrage, and journalists are defamed by their audiences. This form of online aggression occurs predominantly in social-political settings, is highly public, is collective, and targets public actors. Explaining and empirically exploring it is the focus of this dissertation. Compared to the three studies incorporated in this dissertation, the value added by this synopsis is generated by embedding the three studies in an overarching metatheoretical framework and discussing their contributions to it.