The Medication Assisted Treatment (MAT) and Re-entry Initiative was one of several projects funded in 2018 by the Center for Substance Abuse Treatment (CSAT), Substance Abuse and Mental Health Services Administration (SAMHSA) to expand capacity to deliver medications to treat opioid use disorder (MOUD). Nationwide, the Franklin County Sheriff’s Office (FCSO) was the only criminal justice institution to be awarded a grant. The project created a new criminal justice-engaged evaluation and research collaborative in Western Massachusetts that now involves the University of Massachusetts Amherst (UMass), the Hampshire County House of Corrections, and several community-based providers of health and social services. Building on this foundation, the collaborative is now a key component of several NIH-funded research projects. Presenters will provide an overview of the SAMHSA-funded project, report on findings, and present lessons learned from the first year of implementation. This session will also provide guidance on how to launch, sustain, and grow criminal justice-engaged evaluation and research collaboratives.