On Tuesday, all eyes were on America as Barack Obama took over from George Bush and became the 44th US President.
Newsround's Adam was there when Obama won the election back in November.
And he headed back out to Washington as the new president moved into the White House.
Wednesday, 21 January
Obama's face is going on everything!
So after sunny, historic Washington DC I am back in rainy, just-the-same-as-usual London. It's amazing to see that Britain's almost as Obama-crazy as America has been.
As I was leaving the States, his face was still everywhere and on everything. I think the coolest thing I spotted was this Obama-themed skateboard.
Unfortunately it wouldn't fit in my luggage.
While I was taking off, Obama was in the White House taking the oath of office for a second time after he fluffed up the words that officially made him president during the Inauguration. Very weird!
One last look at the Capitol Building
And on the way to the airport, I walked past the Capitol Building where the historic moment happened.
The huge stage in front of it was built specially for the ceremony, but luckily they hadn't taken it down so I could get one last look. Things look more normal around town, but I think people are still really excited under the surface.
Now all the talk is about Obama's first 100 days.
The stuff the new president does in his first few months in office will have a big impact on what the public and the media think of him. So look out for some big announcements coming soon.
Tuesday, 20 January
Adam reporting for Newsround - check out the queues behind him
Phew. What a day!
Everyone had told me that the day Barack Obama took over as President would be crazy. They were all right.
All the best spots that were near the Pres or with good views of the action were gone by four 'o'clock... IN THE MORNING!
Luckily I had a good view of the Capitol Building where the ceremony was taking place at midday.
And it was exceptionally exciting when Obama officially took over as President right in the middle of Newsround.
The ceremony was emotional
The ceremony was pretty emotional. Apart from the bit where Barack Obama slightly mucked up the words for the oath of office - the most important part of the whole day!
There were people everywhere.
And I mean everywhere. It took ages to get from place to place.
But there was plenty to take in. Like the Obama supporter dressed up as him in a padded superhero costume, or the guys who could do a kind of breakdancing with giant Barack Obama signs.
Then came the Presidential Parade. It lasts for a few hours and so I decided to watch it on TV over a cheeseburger.
I was really proud when I saw my friends from Punahou School right near the start.
Barack Obama looked pretty pleased to see his old school, too.
President Barack Obama and First Lady Michelle Obama
Now all of Washington seems to have swapped its hats and scarves for bow ties and ball gowns.
Loads of people are going to balls to welcome the new president.
Barack Obama and his wife Michelle are dropping in on TEN of them in one night.
Luckily they have a couple of stretch limos and a 200(ish)-strong police escort and so they don't have to worry about the traffic too much.
The Inauguration has been amazing. I've been to Washington twice before, but it's been turned totally upside-down for the last few days.
I can't wait to see if President Barack Obama's going to shake up the country, and the world too.
(PS Have you noticed that I haven't said the word "historic" today? I've used it soooo many times that I am trying to cut back!)
Monday 19 January
The marching band from Obama's old school get in some practise
This morning I met up with some people who are going to get VERY close to Barack Obama during the Inauguration: the marching band from his old school in the island state of Hawaii.
After he officially becomes President there is a big parade, with more than 90 groups taking part.
His old school, Punahou High are going to be really near the front. They will march past Obama and salute him outside the White House.
Adam's sign couldn't be missed!
They are all feeling pretty excited and quite nervous. Hawaii is really hot and they are worried that their instruments are going to freeze and bits might fall off in the cold of Washingtion DC.
I also caught up with Queen Mary of Peace School, whose pupils have travelled from the southern state of Louisiana to get here.
They had to take two flights just to get to Washington but they all thought it was going to be worth it.
Everyone's being warned about the crowds and the big queues because of all the security.
Pupils took two flights to get to Washington but all said it was worth it
The guys from Louisiana are going to be leaving their hotel at 4AM so they can get a good spot for the ceremony, which starts 7 hours later!
And I got to see Obama at last. Well... kind of.
He just popped into the hotel across the street from where I am staying. I say "popped in" but you can't really do that when you travel in a huge bullet-proof limo surrounded by bodyguards and all the roads are closed off!
It was definitely very exciting, though.
Sunday 18 January
Adam outside Independence Hall
In two days, the new president takes office. I decided to visit the historic city of Philadelphia where the job of President was first invented.
Over 200 years ago a document called the Constitution was written here. It spelt out what the president had to do and how the American government would work.
It was put together in a building that's now called Independence Hall. And I'm not the only one who visited over the weekend. Barack Obama was in town too.
He took a special presidential train ride from Philadelphia to his new home town Washington DC, waving to people along the way.
I spoke to some kids about their new leader. Most of them were really excited and think this is a great moment of history because on Tuesday they get to see the first African American become president.
Adam met loads of kids bowling
Then I decided to chill out by going bowling. I found a really cool bowling alley and chatted to some kids about the inauguration.
They say things have felt a bit different in the US since Obama won the election. And I got to taste victory too when I scored a (very fluky) strike!
Sadly, the Philadelphia Eagles American football team didn't have any luck. They lost out on a place in the Superbowl. Loads of people at the train station were watching the game.
Then it was time for me to get on board to head to Washington DC.
When I arrived here the city was packed because thousands of people had been to the famous Lincoln Memorial for a special concert to welcome Barack Obama.
There's definitely a massive party vibe. And it's only going to get bigger as millions of people start arriving over the next few hours.
Saturday 17 January
I am off to America again to see Barack Obama make history (again)!
Adam at the airport
Last year he became the first black man to win a presidential election. Now he is officially taking over.
He will be moving into the White house on Tuesday after a massive ceremony in Washington DC called the Inauguration.
One guess is that five million people will turn up to watch it happening because it's so historic.
I'll be reporting on it all for Newsround.
I'm really excited about it, but I've been warned that it's going to be freezing so have packed my thermal underwear!
I'm at the airport now so next time you hear from me I will be stateside.