From Longman Dictionary of Contemporary English9-11 Commission9-ˈ11 Comˌmission 🔊 🔊 a US commission (=group of people who have been given the officialjob of finding out about something)set up by Congress to examine the actions taken by the US government before, during, and after the terroristattacks in New York City and Washington on September 11,2001. The Commission wanted to find out if the US government knew that an attack might take place and if the government was properly prepared for any attack. It also wanted to establish whether the government acted properly after the attack. It criticized the CIA, FBI, and the US government. The commission was closed in 2004.