PROJECT SUMMARY/ABSTRACT In this application, the current aims of the ABCD Study, including aims that have been added since its onset through supplemental funding, and the resulting longitudinal data resources developed to date, are described; and a plan to explore the potential of the study and these data resources for enhancing knowledge relevant to HIV is outlined. In brief, the plan is to convene a meeting of leading HIV researchers with ABCD investigators and NIH collaborators (including from the HIV Research Program) to determine if and what opportunities exist to leverage the ABCD Study to fill research gaps that may exist in current knowledge relevant to HIV risk, exposure, or treatment. The goal of the meeting is to identify specific feasible modifications or additions to the study, or other strategies, for addressing these issues, and to evaluate their significance.