Barack Obama is getting to work in his first day of his new job as president of America.
Millions of people around the world watched as Obama took something called the oath of office on Tuesday, to officially take over from George Bush.
After the day's ceremonies the parties began, and President Obama attended celebrations late into the night.
But the hard work has already begun with the new president getting ready for some important meetings.
On his first full day in the Oval Office, Mr Obama will meet financial experts to discuss the cash problems facing America, and the world.
President Obama celebrated late into the night
He will also be talking to security experts and military officials.
In his speech on Tuesday, Mr Obama said he wanted to bring in a time of peace.
"We will begin to responsibly leave Iraq to its people, and forge a hard-earned peace in Afghanistan," he said.
But it's not just President Obama who's beginning a whole new way of life.
His daughters, Malia, 10, and Sasha, 7, have also had their whole lives turned upside down too.
It's hard to imagine what it's like when your dad becomes one of the most important men in the world.
But George Bush's daughters have been through it all before when their dad was president.
Barbara and Jenna have been passing on some advice to the younger girls in a letter printed in a newspaper.
The 27-year-old twins told Malia and Sasha to make the most of everything and have fun, but to remember who their dad really is.