Committees of Visitors (COVs) meet once every three years to review the program portfolios of NSF divisions, but COVs may also be constituted to review groups of programs that stretch across divisions, or Foundation-wide crosscutting programs such as CAREER and ADVANCE. COV reviews provide NSF with external expert judgments in two areas: (1) assessments of the quality and integrity of program operations and program-level technical and managerial matters pertaining to proposal decisions; and (2) comments on how the results generated by awardees have contributed to the attainment of NSF's mission and strategic outcome goals. COV reports and the NSF responses to those reports may be found at: https://www.nsf.gov/od/iia/activities/cov/covs.jsp.