US President Barack Obama is set to begin his second term in charge of the country.
Hundreds of thousands of people attended a special ceremony in Washington, called an inauguration.
The president made a public oath and a big speech outlining his plans for the next four years. Beyonce sang the US national anthem at the event.
Obama became America's first black president in 2009 and was re-elected last November.
'Preserve, protect and defend'
The president was already officially sworn in at a small White House ceremony on Sunday because US law says it needs to happen by 20 January.
He rested his hand on a Bible used for many years by his wife's family and vowed "to preserve, protect and defend the Constitution of the United States".
At Monday's public event he spoke about what he wants to achieve over the next four years.
Watch Joe's report on the big issues facing Obama in his second term by clicking on the video above.