The 20th anniversary of the 9/11 terrorist attacks started in New York and was held at the Pentagon and Shanksville crash sites near Washington DC.
President Joe and Bidens attended a memorial service at Ground Zero, the site of the former World Trade Center in New York, where the first attack was struck 20 years ago.
In a video message released the night before the memorial service, President Biden said, "I will never stop protecting the people."
Leaders from all over the world also paid tribute to the victims and said, "We will never forget the past."