Complete coverage: How 9/11 changed America, and the world
Presidents Joe Biden, Barack Obama and Bill Clinton all gathered at the site where the World Trade Center towers fell two decades ago.
Twenty years ago, the 11th of September dawned as just a date. By midnight, it was 9/11, the staggering starting point for a new era of terror, war, politics, patriotism and tragedy.
In the ghastly rubble of Ground Zero's fallen towers 20 years ago, Hour Zero arrived, a chance to start anew.
Twenty years on, the skepticism and suspicion first revealed by 9/11 conspiracy theories has metastasized, spread by the internet and nurtured by pundits and politicians.
In the aftermath of 9/11, America was introduced to an array of personalities. Some we had known well. Others were thrown into the spotlight. Where are they now?
The worst terror attack on American soil led to increased and sometimes tension-filled security measures in airports across the world, aimed at preventing a repeat of that awful day.
Sept. 11 survivors bear scars and the weight of unanswerable questions. On the 20th anniversary of the attack, six survivors reflect on their journey since that tragic day.
In November 2001, in a mostly ruined Afghan capital, America's mission after the 9/11 attacks brought hope to many Afghans. Much has changed from that moment to today.
Before social media and with online news in its infancy, the story of 9/11 unfolded primarily on television. These three newsmen were where most Americans turned.