Abstract Online aggression and trolling have become persistent features of contemporary digital interaction, shaping individual well-being and the quality of public discourse. This secondary data-based research paper examines how anonymity and deindividuation contribute to online aggression, with a particular focus on the behavior of trolling. Drawing on established psychological frameworks, particularly the Online Disinhibition Effect and the Social Identity Model of Deindividuation Effects (SIDE), the paper synthesizes evidence from peer-reviewed research and large-scale survey findings. Anonymity is argued to reduce accountability and heighten disinhibition, while deindividuation shifts attention away from personal standards toward situational cues and group norms. Secondary statistics indicate that online harassment is widespread, with substantial proportions of users reporting direct exposure to name-calling, threats, stalking, and sexual harassment. The synthesis suggests that anonymity does not inevitably produce aggression; rather, it interacts with platform design, perceived norms, peer reinforcement, and individual traits (e.g., sadism/psychopathy). The paper concludes with implications for prevention, including “identity-light but accountability-strong” platform design, norm-setting interventions, and bystander empowerment.