instmctions): The Population Core (PC) has been established to develop, manage, and retain the various population resources needed to achieve the objectives of the Research Projects and future pilot and developmental projects. The research projects in the USC TCORS draw, in part, upon participants in previously-developed cohort populations. However, each project will also need to expand upon or renew contact with established population resources to succeed. Additional populations have also been identified for several pilot projects being considered within the TCORS. These diverse and complementary population cohorts will be substantively supported and managed within the proposed Population Core. The Population Core will be staffed to provide tracking and retention of existing cohorts, recruitment of new cohorts, and outreach and networking to identify new populations for future research projects, including those initiated through the Pilot Projects Program Core. An experienced team has been assembled to efficiently meet these objectives. RELEVANCE (See instructions): The Population Core will support activities of the USC TCORS, helping it to efficiently track existing study participants and to identify new ones.