Assertive Community Treatment (ACT) is now recognized as the model proven to be most successful in working with clients with long-term, severe mental illness. The first documented research replication study of ACT was Harbinger of Grand Rapids, in Kent County, Michigan. The Harbinger program influenced significant programmatic changes throughout the public mental health system in Michigan. This paper describes this evolution in community mental health locally and why these changes came about. The state-level strategy to implement replications of Harbinger is described, as well as funding and monitoring mechanisms that have now resulted in over 100 successful ACT programs in Michigan. For mental health administrators, the implications discussed include the future of ACT promotion and implementation, within the reality of a managed care framework.