met the scientific milestones and feasibility requirements may transition to the UH3 phase. The UG3/UH3 application must be submitted as a single application, following the instructions described in this FOA. The UG3 phase will permit both scientific and operational planning activities. Scientific planning activities include small-scale data collection to assess the feasibility and/or acceptability of a planned behavioral or social intervention and associated study procedures (e.g., acceptability of study content or mode of delivery; feasibility of proposed data collection procedures; preliminary testing of intervention training and fidelity monitoring procedures). Operational planning activities include, at a minimum, development of: the final clinical protocol; the intervention manual or equivalent; the data management system and other tools for data and quality management, safety and operational oversight plans; recruitment and retention strategies; and other essential documents. The UH3 phase will support the conduct of investigator-initiated intervention research at all stages, from early mechanistic research and intervention development (e.g., Stages 0/ I) through implementation and cost-effectiveness research (Stages IV/V).