This comparative case study investigates the voluntary sector interface with criminal justice systems for youth and young adults in England/Wales and Finland. Methods included document review and stakeholder interviews. Across cases, key differences were found in the training of corrections and probation officers, funding sources and structures, and use of actuarial models and evidence. The organization of these relationships was also different for youth and young adult services, particularly in England/Wales where clear lines are drawn between age groups. The results contribute to an understanding of how system-level factors can drive relationships between the voluntary and criminal justice sectors.