In New York, family members of the victims, many carrying pictures of their loved ones, joined Vice President JD Vance and four former US presidents at Ground Zero in Lower Manhattan.
The ceremony began, as always, at 8:46 a.m. ET (1246 GMT) with a moment of silence to mark the instant when American Airlines Flight 11 struck the World Trade Center's North Tower in what would become the deadliest attack ever on US soil.
Shortly after, victims' family members began reading aloud the names of all 2,977 people who died on September 11, as well as the six people killed in the 1993 World Trade Center bombing.
Other moments of silence followed to mark when the other three airplanes crashed and the two towers collapsed. For the first time, a seventh moment of silence honored the thousands who have died since 2001 from illnesses tied to the toxic dust that poisoned the air for months afterward.
At the Pentagon, where American Airlines Flight 77 struck the building's west flank, killing 184, President Donald Trump said, "We salute our first responders and law enforcement, and we love them.”
Mourners also gathered in Shanksville, Pennsylvania, at the crash site where passengers brought down one of the four hijacked jetliners, United Airlines Flight 93, that had been headed for Washington.
