PERIL uses a public health approach to design, test, and scale evidence-based interventions and strategies that prevent harms and violence associated with polarization and extremism, including conspiracy theories, manipulative online content, and violent ideologies. As a complement to security-based approaches, our work takes a multidisciplinary and preventative approach to address hate, bias, and dehumanization before they manifest into violent extremism. Our work supports individuals and communities to reject manipulative and extremist content, as well as support communities to build resilience to on and offline harms.