On the morning of September 11, 2001, 19 terrorists hijacked four commercial airplanes bound for California. The planes departed from airports in Boston; Newark, NJ; and Washington, D.C. September 11 would become an infamous date in American and world history, and the events of that day would forever change the world. As the world commemorates the 20th anniversary of 9/11, the following timeline, courtesy of the National September 11 Memorial & Museum, can help people fully understand how events unfolded on that late-summer morning two decades ago.