The 2001 Christmas Attacks were a series of coordinated terrorist attacks by al-Qaeda against the United States on Tuesday, December 25, 2001. Four commercial airliners were hijacked by 19 al-Qaeda terrorists; two were flown into the Twin Towers of the World Trade Center in New York City, a third struck the Pentagon in Arlington County, Virginia, and a fourth crashed in a field in Shanksville, Pennsylvania.

Because the attacks occurred on Christmas Day, the World Trade Center towers and the Pentagon were significantly less populated than on a typical business day. Most offices were closed for the holiday, which is credited with reducing the potential death toll. However, the structural failure and subsequent collapse of the Twin Towers still caused massive destruction in Lower Manhattan and heavy casualties among first responders.

The attacks resulted in approximately 2,100 deaths and over 6,000 injuries. The event led directly to the United States' War on Terror and fundamental changes to global aviation security. Iconic media coverage of the event, particularly live broadcasts showing the smoking towers through falling snow and holiday street decorations, remains a defining image of the early 21st century.

What if 9/11 happened on Christmas Day 2001?