Events are taking place at the sites of the attacks — in New York City, Washington DC and Shanksville, Pennsylvania — and elsewhere around the nation to honor the 2,977 people killed that day.
The main ceremony is being held in New York, where Islamists from the group flew two hijacked commercial airliners into the twin towers of the city's famous World Trade Center — a symbol of American economic power.
New York Mayor Zoran Mamdani, Governor Kathy Hochul and former Presidents Bill Clinton, George W. Bush, Barack Obama and Joe Biden are in attendance as well as current Vice President JD Vance.
Friday's event will feature wreath layings and vigils, punctuated by several moments of silence, marking the moments of impact and collapse and honoring the memory of the dead.
Family members will read out the names of the people killed that day, as well as six that were killed in a 1993 al-Qaeda bombing in the building's basement.
This year, the ceremony also acknowledged more than 600 firefighters who died from illness related to the toxic air and dust emanating from the burning structures of the site.
In Washington, President spoke at a ceremony at the Pentagon, the symbol of the US' military might, which was also targeted with a hijacked airliner that day.
In his remarks, Trump referenced , saying the US will never forget 9/11, adding, "that's why we fight today. "
Other administration officials are headed to the Flight 93 National Memorial in Shanksville, Pennsylvania. It was there that passengers stormed the cockpit of a hijacked United Airlines jet in midflight, forcing the plane to crash in an empty field and keeping attackers from hitting their final target, the US Capitol.
25 years later: Keeping the memory of 9/11 alive
European Commission President underscored the strength of democracies, pointing out that the attackers had failed to rob democratic nations of their freedom.
NATO Secretary General Mark Rutte posted on X that allies had, "stood together" that day, "invoking Article 5 for the first and only time in NATO's history. "
Rutte added, "America's friends and allies in NATO stood with you then and we stand with you today. "
US President Trump has often and to helping the US in times of need.
How did the 9/11 terror attacks shape modern America?
America's reputation suffered as a result of and "enhanced interrogation" at secret CIA prisons, as well as its creation of a , where suspected terrorists were held for years in dystopian conditions without trial.
The aftereffects of the wars are still costing the US billions and the debacle of Iraq irreparably damaged the solidarity the US was shown in the immediate aftermath of 9/11.
The attacks changed airport security measures, as well as the US government's ability to surveil citizens — leading to the creation of the Department of Homeland Security, one of the biggest agencies in the US government, and passage of the Foreign Intelligence Surveillance Act (FISA) and the USA Patriot Act.
Further, the event dramatically changed attitudes towards Muslims.
There was much controversy this year over whether Mamdani, for instance, should attend the New York ceremony. Republicans argued against it but the mayor insisted he would do so out of love of city and country and respect for those who died that day and in the years after.
This year's ceremony honors those who have died in the aftermath of the attack
Mamdani's election as mayor shows just how far parts of the country have come since that day and the young Muslim Democrat this week opened a new chapter in the story of 9/11 by releasing tens of thousands of documents showing that .
As asbestos and toxic smoke blanketed the city for months officials told residents and clean-up workers that they had nothing to fear.
In fact, the toxicity of dust, rubble and smoldering plastic and metal has led to at least 9,400 additional deaths according a federal medical monitoring program.
