PROJECT SUMMARY/ABSTRACT (LONGITUDINAL NETWORKS CORE) The long-term goal of the Longitudinal Networks Core (LNC) is to serve as a sustainable resource for the Rural Drug Addiction Research (RDAR) Center, the University of Nebraska, and other academic researchers to inves- tigate substance use/misuse and to address the etiology, assessment, prevention, and treatment of this critical public health challenge. The LNC was designed to meet a pressing need for cost-effective access to long-term recruitment and retention services capable of maintaining a study cohort and to provide expertise in community- engaged approaches and network designs. In Phase 1, the LNC supported researchers from a wide range of disciplines and created the critical infrastructure for managing projects, data, and software use. The goal of the LNC in Phase 2 will be to maintain and extend: 1) access to a longitudinal cohort of people who use drugs from which to recruit study participants; 2) data describing factors affecting regional patterns of substance use; 3) use of LNC software to collect responsive fine-grained data from participants; 4) support for network sampling or analytic approaches; and 5) consultation in community-engaged research, field-based biospecimen testing, ep- idemiological data collection, respondent driven sampling, intervention design, and research with hard-to-reach populations. By offering resources and expertise that do not otherwise exist in the region and would be prohibi- tively expensive for early-stage investigators, the LNC will achieve its vision of increasing substance use/misuse research by elevating research capacity throughout Nebraska. The RDAR Center’s strong collaborations with university-wide research centers, campuses across the University of Nebraska system, and statewide and na- tional IDeA-program partners will be leveraged to expand services and the user base in Phase 2. Towards this end, the LNC will establish, maintain, and expand the Core’s active regional longitudinal cohort of people who use drugs (Aim 1). In doing so, the LNC will provide researchers access to a Participant Pool for recruitment into affiliated projects such as context-sensitive samples for biological and epidemiological research and inter- vention trials and secondary data for novel network approaches to understanding regional patterns of substance use. The LNC will also expand the user base of LNC services (Aim 2) by leveraging the Phase 1 success of software platforms developed by the LNC to enable innovative research in community settings. LNC services will facilitate the transition of early-stage investigators to independence, the development of interdisciplinary teams, and the successful pursuit of large external funding within RDAR’s thematic focus. These endeavors, in turn, will grow an already impressive concentration of expertise for substance use and related health disparities research and cultivate collaborations nationally through existing IDeA-s...