Public mental health authorities have access to large administrative databases. Advances in information technology now make it possible to use secondary analyses of these data to inform policy and clinical interventions. New York City and State mental health authorities developed an initiative using Medicaid claims and other administrative data to identify individuals with serious mental illness living in New York City (NYC) who are at risk of lapses in care. The NYC Mental Health Care Monitoring Initiative represents one of the first efforts to create "evidence-based policy." The authors describe the initiative's background, development, and key collaborations.