A 2018 Massachusetts law (“Chapter 208”) established a 4-year pilot program to expand the use of all FDA-approved forms of medications for opioid use disorder (MOUD) at five county jails; two additional jails voluntarily joined this pilot. The law stipulates that MOUD be maintained in individuals who were already receiving it prior to detention; initiated prior to release from jail when appropriate; and continued in the community via facilitated linkages to local services after release. The Massachusetts Hub will conduct a longitudinal treatment outcome study of individuals in these jails to examine MOUD initiation, engagement and retention, as well as fatal and non-fatal overdose and recidivism. The study will also identify strategies associated with the successful implementation of MOUD.