Barack Obama is sworn in as America's 44th president - and its first African-American leader - in a ceremony in Washington DC watched by millions around the world.
Millions of people in the US and around the world watched as he pledged to "preserve, protect and defend" the US constitution.
The new president was joined on stage by his wife Michelle and his young daughters Sasha and Malia, who will be the youngest White House residents for many years.
Security was intense, with roads and subways closed and some 40,000 security personnel on duty, including police snipers in position on the roof of the White House.
