Advancing Peer-Delivered Mental Health Interventions for Young Adults with Intellectual and/or Developmental Disabilities: Adapting and Testing StepUp Peer Programming - Young adults with intellectual and/or developmental disabilities and co-occurring mental health conditions (YAIDD-MH) report a lack of access to mental health supports, a critical concern, given the high rate of mental health challenges experienced by YAIDD. There have been recent calls to address this service gap by recognizing the potential of nonprofessionals to effectively deliver mental health interventions. Peer-delivered services are hypothesized to be uniquely effective because individuals with shared disability experiences can provide support distinct from professionals. In our previous research, we identified that YAIDD-MH can serve as peer mentors, delivering a mental health intervention with high fidelity. However, this intervention was too resource intensive to translate to community settings. Our goal is to adapt StepUp, a low-resource mental health intervention, for peer delivery by YAIDD-MH in the United States. We will also study the feasibility of StepUp Peer with the broader goal of increasing access to evidence-based mental health supports for this group. Our objectives are: 1) Adapt StepUp for peer delivery by YAIDD-MH in the United States; 2) Conduct a feasibility study of StepUp Peer to evaluate acceptability, the supervision model, and needed revisions for community-based delivery; and 3) Conduct a pilot-randomized waitlist control to evaluate feasibility of trial methods and preliminary outcomes. The primary anticipated outcome is new knowledge about the feasibility and potential promise of a peer-delivered mental health intervention in community-based settings; this knowledge will contribute to future work addressing Health and Function for YAIDD-MH. Products will be the adapted StepUp Peer protocol and intervention materials.