Communities want to reimagine models of emergency responses to individuals experiencing a crisis. But the paucity of research in this area means policymakers have little access to data to inform their decision-making. In this white paper, we summarize the types of first responder-led, emergency-response models and present the evidence that exists for them. Then we suggest investment to fill the evidence gaps, support reform efforts, and ensure that reimagining the emergency response system both contributes to and relies on evidence.