We use a public health approach to design, test, and scale-up evidence-based tools and strategies that effectively reduce the threat of radicalization to harmful online and offline content including conspiracy theories, mis/disinformation, propaganda, and supremacist ideologies. As an alternative to security-based approaches that rely on surveillance, censorship, and incarceration, our work takes a multidisciplinary and pre-preventative approach to address hate, bias, and radicalization before they manifest into violent extremism. Our work supports individuals and communities to reject propaganda and extremist content, as well as empower them to intervene and interrupt early radicalization.