Official time is time spent by federal employees performing certain union representational activities, such as negotiations and handling grievances. Employees on official time are treated as if they are in a duty status and are paid accordingly. OPM’s estimated total payroll costs, salary and benefits, for fiscal year 2012 official time hours was over $156 million and covered more than 1.2 million employees. GAO was asked to review federal rules relating to the use of official time. This report (1) describes the extent of official time use by 10 selected agencies; (2) assesses OPM’s cost estimate for official time; and (3) examines OPM’s reporting on official time. GAO obtained usage data from agencies and OPM’s annual reports. For this study, GAO selected 10 agencies (National Science Foundation, Railroad Retirement Board, Social Security Administration, and the Departments of Commerce, Health and Human Services, Homeland Security, Labor, Treasury, Transportation, and Veterans Affairs) representing 47 percent of BU employees covered by OPM’s report. GAO’s selection was based on factors such as agency size, number of BU employees, and official time rate.