This guide provides practical, evidenced-based strategies and public health approaches, resources, and program models that first responder agencies, their partners, and communities can use to implement or expand practices and approaches for linking people to substance use services. It describes the key role first responders play in encountering those with substance use disorders (SUD), the skills needed to help those in an overdose situation, public health approaches to those with SUD, guidance on implementing first responder initiatives, and resources for such initiatives.