The treatment of transitioning youth (ages 16-25) diagnosed with co-occurring mental health and substance abuse problems has been the focus of numerous research and practice efforts. However, far less attention has been devoted to intervening early to address alcohol and other drug (AOD) use, which has the potential to contribute to the numerous challenges transitioning youth with emotional or behavioral disorders already confront. This article describes transitioning youth, their need for AOD early intervention, and the community mental health system characteristics to be considered in developing early intervention practices. Implementation and enhancement of effective AOD screening and early intervention practices has the potential to facilitate a healthy transition to adulthood for youth who experience considerable risk for substance abuse disorders. (Published Abstract)