Cornerstone centers on addressing three pressing problems: (1) the discontinuation, or at best fragmentation, of mental health care for TAYMD, (2) the lack of evidence-based interventions for TAYMD, and (3) the reality that promising practices for TAYMD, many of which Cornerstone builds upon, have not been tested with a sample that moves from child to adult services. Cornerstone deals with these problems in innovative ways at a time of transformation in health care. First, Cornerstone provides a 'boundary spanning case manager' (BSCM) across the transition. That is, rather than extending the age of service provision in the child system, we prioritize collaboration with the adult system and practical assistance to assure that the transition to developmentally and clinically appropriate adult services and independent adulthood happen at age 18. Second, Cornerstone incorporates an innovative form of social support, namely a recovery role model mentor (RRM) who is a decade older than TAYMD. The RRM co-facilitates weekly groups and provides important information and mentoring (i.e., modeling, connection) for TAYMD. Third, the development of Cornerstone is aligned with policy and practice transformation, particularly Affordable Care Act and New York State Medicaid Redesign, prioritizing coordinated, evidence-informed care for TAYMD, expansion of the workforce, and an emphasis on achieving functional outcomes and wellness.