EMS encounters for opioid overdose and withdrawal have escalated along with the national opioid use disorder (OUD) crisis. Despite the efficacy of buprenorphine treatment for patients with OUD, and effectiveness of initiation of buprenorphine in the emergency department (ED) setting, the treatment gap remains wide. Emergency Medical Services (EMS) is often the first encounter a person with OUD has with the healthcare system, either after overdose reversal or for treatment for moderate to severe opioid withdrawal. Unfortunately, some patients refuse transport, or leave against medical advice once they arrive in the ED. Thus, buprenorphine offered as out-of-hospital emergency care could provide a vital strategy opportunity for initiation of life saving treatment and referral for ongoing OUD care. Current evidence for EMS initiated buprenorphine is limited to small retrospective or nonrandomized prospective cohort studies. While promising, these studies suffer from lack of intervention fidelity, bias, and uncontrolled confounders. EMS-based research has the potential to expand the reach of ED- and outpatient-based OUD interventions, and significantly enhance availability of evidence-based addiction care into settings where preventing adverse consequences of untreated opioid use is critically important. During the 8-month project period, our Specific Aim is to: Develop a study protocol for prehospital EMS-initiated buprenorphine treatment for patients with OUD presenting with (a) overdose requiring a naloxone reversal or (b) acute opioid withdrawal to promote engagement in OUD treatment. Our approach will use a Delphi Consensus Method with a panel of emergency medicine, EMS, and OUD care content experts. The study protocol will be refined through subsequent focus groups with EMS personnel and patients with OUD to ensure protocol feasibility and acceptability. Over subsequent study years we will conduct a sequence of pragmatic controlled field studies to test implementation of the protocol, followed by a randomized trial to evaluate the effectiveness of EMS delivered buprenorphine on linkage to addiction treatment.