When federal agencies and programs lack appropriated funding, they experience a funding gap. Under the Antideficiency Act, they must cease operations, except in certain emergency situations or when law authorizes continued activity. Failure of the President and Congress to reach agreement on interim or full-year funding measures occasionally has caused government shutdowns, the longest of which lasted 21 full days, from December 16, 1995, to January 6, 1996. Government shutdowns have necessitated furloughs of several hundred thousand federal employees, required cessation or reduction of many government activities, and affected numerous sectors of the economy. This report discusses the causes, processes, and effects of federal government shutdowns, including potential issues for Congress.