While online radicalization and recruitment have occurred for years, today’s online ecosystems of harm are particularly troubling and concerning. This training provides an overview of online nihilistic violent extremist (NVE) networks and spaces, focusing on prominent networks such as the True Crime Community (TCC) and 764. It explains what these networks are, clarifies common misconceptions surrounding their nature, participants, and goals, and examines where and how individuals are drawn into these spaces. The presentation further analyzes how preexisting vulnerabilities are actively exploited within these environments, including deliberate recruitment and grooming efforts in online mental health-related communities. It concludes with an overview of key behavioral warning signs and indicators that caregivers and practitioners should watch for.