President Barack Obama took the ceremonial oath of office, Monday morning.

Up to 900,000 people were expected to watch the ceremony, in person, outside the U.S. Capitol building.

That’s about half the amount that filled the National Mall for the first one, four years ago.

President Obama was actually sworn into office on Sunday.

That’s because the U.S. Constitution says that the President must be sworn in by January 20th.

So U.S. Supreme Court Chief Justice John Roberts had President Obama recite the oath at the White House.

That was held in the Blue Room, which is an oval-shaped reception space in the president’s official residence.

It was witnessed by First Lady Michelle Obama and daughters Malia and Sasha, where he was joined by his wife, Michelle, and his two daughters Malia and Sasha.

Vice President Biden was also sworn in, at a separate event.

Justice Sonia Sotomayor performed the honors at Biden’s home at the Naval Observatory in Washington.