What group was behind a terrorist attack in the US on September 11 2001?

The terrorist attacks on September 11, 2001, were carried out by the Islamist extremist group al-Qaeda. Led by Osama bin Laden, al-Qaeda orchestrated the hijacking of four commercial airplanes, two of which were flown into the World Trade Center in New York City, while another hit the Pentagon, and the fourth crashed in Pennsylvania after passengers intervened. This coordinated attack resulted in significant loss of life and had profound implications for U.S. domestic and foreign policy.