In the video player above, watch firsthand accounts from those who were in Lower Manhattan on that fateful day, with commentary from then-anchor Bill Beutel. (Warning: This contains images that some may find disturbing.)
Each year, relatives of the victims descend on ground zero in Lower Manhattan, and the events of that terrible day and the weeks, months and years that followed are never forgotten, nor are the memories of those killed by terrorists in hijacked planes.
9/11 Timeline: How the September 11 attacks unfolded
Additionally, we remember all those who have died from 9/11-related illnesses from their heroic work at ground zero and those who suffer today.
September 11 still shapes American policy, politics and everyday experiences in places from airports to office buildings, even if it's less of a constant presence in the public consciousness after more than two decades.
WATCH: How a reporter and photographer escaped the Twin Towers collapse
How reporter N.J. Burkett and his photographer escaped Twin Towers collapse
The 9/11 commemorations are by now familiar rituals, but each year at ground zero, victims' relatives infuse the ceremony with personal messages of remembrance, inspiration and concern.