As the tenth in the Completing College series, this report updates the six-year college completion rates nationally and by state, by tracking the enrollment and completion outcomes for the fall 2015 cohort of beginning college students through June 2021. The national completion rate measures the performance of the entire higher education system. It counts all students who enter postsecondary education for the first time each fall, enrolling full-time or part-time at two-year or four-year institutions, and completing at any U.S. degree-granting institution. It includes those who complete after transfer, not just completions at the starting institution. Thus, the results more fully capture today's students' diverse pathways to success, which increasingly involve mobility across institutions and across state lines, re-entry after stop-out, and changes in enrollment intensities. Newly added this year, the longitudinal data dashboard offers detailed six-year completion outcomes by cohort year across starting institution sectors and student backgrounds, enabling national and state-level comparisons through interactive visualizations and analysis tools. Underlying data are available online for downloading. [Title varies: "Completing College: National and State Report on Six-Year Completion Rates for Fall 2015 Beginning Cohort (Signature Report 20)."]