This mixed method study examined current practices and barriers for screening and assessing substance use among youth/young adults in community mental health systems. Substance use rates remain high among youth/young adults in the general population and substance use disorders are prevalent among young people involved in public service systems such as mental health. In an effort to understand the dynamics for early intervention, 64 case managers and/or clinical directors from children’s mental health systems in two states participated in an online survey or focus group in fall 2008. Quantitative survey questions and qualitative focus group questions explored attitudes and perspectives about screening and early intervention for substance use among youth/young adults involved in the mental health system and current agency practices. Mixed method results suggest a number of barriers to substance use screening and early intervention and point to innovations that could be more effectively supported.