The September 11, 2001 attacks (often referred to as 9/11—pronounced "nine eleven") consisted of a series of coordinated suicide terrorist attacks upon the United States, predominantly targeting civilians, carried out on Tuesday, September 11, 2001.

That morning, 19 men affiliated with al-Qaeda^[1] hijacked four commercial passenger jet airliners. Each team of hijackers included a trained pilot. Two planes (United Airlines Flight 175 and American Airlines Flight 11) crashed into the World Trade Center in New York City, one plane into each tower (One and Two). Both towers collapsed within two hours. The pilot of the third team crashed a plane into the Pentagon in Arlington County, Virginia. Passengers and members of the flight crew on the fourth aircraft attempted to retake control of their plane from the hijackers; that plane crashed into a field near the town of Shanksville in rural Somerset County, Pennsylvania. Excluding the 19 hijackers, a confirmed 2,973 people died and another 24 remain missing as a result of these attacks