On 20 January, Barack Obama becomes the 44th President of the United States of America. He will take the oath of office here, at the US Capitol Building in Washington DC.
Millions of people are expected to go to Washington for the ceremony. A lot of them camped overnight to get a good spot when the National Mall opened at 4am in America.
It was pretty hard to keep warm at times. Some gathered around steam vents to try to keep out of the cold.
Lots of people could be seen gathering on the National Mall early in the morning on Tuesday. Public transport was already really busy at 5am!
They won't be able to see Obama become president in person though. They'll have to watch him take the oath of office on giant video screens like this one.
It's not just members of the public crowding into Washington. Journalists from all over the world are also in the American capital to report on Obama becoming president.
And those reporters have got plenty of people to talk to, as the crowds build ahead of the ceremony, called an inauguration.
The crowds used any spot they could to get a good view, including climbing up high onto this statue. Let's hope they're holding on tight - that river looks cold!
Before heading to the main inauguration ceremony Barack Obama and his wife Michelle went to a church in Washington.
And then they stopped in at the White House to say goodbye to President George W Bush and his wife Laura. They will live in Texas after handing the White House keys to the Obamas.