With overdose deaths increasing, improving access to harm reduction and low barrier substance use disorder treatment is more important than ever. The Community Care in Reach model uses a mobile unit to bring both harm reduction and clinical care for addiction to people experiencing barriers to office-based care. These mobile units provide many resources and services to people who use drugs, including safer consumption supplies, naloxone, medication for substance use disorder treatment, and a wide range of primary and preventative care. This protocol outlines the evaluation plan for the Community in Care model in MA, USA. Using the RE-AIM framework, this evaluation will assess how mobile services engage new and underserved communities in addiction services and primary and preventative care.