ABSTRACT Opioid overdose is a major cause of death among people experiencing homelessness. Although buprenorphine treatment is effective for opioid use disorder (OUD), homeless persons experience multiple barriers to accessing this life-saving medication. Recently, the FDA approved a once-monthly injectable extended-release buprenorphine formulation for treatment of OUD, which may offer an alternative to sublingual buprenorphine for populations challenged by adherence, such as homeless persons. Long-acting formulations of buprenorphine treatment hold promise for improving adherence, retention, and clinical outcomes. However, little information exists about how amenable out-of-treatment homeless persons with OUD may be to an injectable buprenorphine formulation. Furthermore, although buprenorphine treatment can occur in a variety of settings, limited research has measured readiness of system models of care for the treatment of OUD among homeless persons. This project aims to assess individual, provider and system-level barriers and facilitators to accessing buprenorphine treatment among homeless people with OUD. Guided by the Consolidated Framework for Implementation Research, we will use an exploratory sequential mixed method design to identity potential individual, provider, and system-level barriers to implementation of buprenorphine treatment in two service settings: homeless shelters and syringe access programs. The specific aims of the project are: (1) assess organizational capacity and organizational readiness for the expansion of buprenorphine treatment in homeless shelters and syringe access programs; and (2) assess willingness of homeless people with OUD to receive buprenorphine treatment, preferences for different buprenorphine treatment formulations (sublingual vs. injection), and identify factors associated with preferences for buprenorphine treatment formulations. To achieve Aim 1, we will conduct in-depth interviews, focus groups, and surveys with health care providers, program staff, and program directors working at homeless shelters and syringe access programs. In Aim 2, we will recruit 200 homeless persons from homeless shelters, syringe access programs, and homeless encampments; and then administer structured surveys to identify preferences for buprenorphine treatment formulations, and identify predictors of preferences for different buprenorphine treatment formulations. Researchers can use the results of this study to inform the planning of buprenorphine treatment for out-of- treatment homeless persons with OUD, and we will use these results to conduct a subsequent feasibility and acceptability trial of sublingual buprenorphine vs. extended release buprenorphine to treat OUD in homeless persons.