Terrorists who hijacked four commercial airliners killed nearly 3,000 people on Sept. 11, 2001, most of them when the attackers struck the World Trade Centers' Twin Towers. 

On Saturday, surviving family members at Ground Zero in New York City, the site of the WTC attacks, will read the names of those whom they lost, starting at 8:40 a.m. ET.

You can watch the 20th anniversary commemoration ceremonies above or by clicking the player below.