Hundreds of teenagers have kicked the UK's politicians out of Parliament for the day to have their own debate.
They're all members of something called the UK Youth Parliament, and they haven't really taken over for a day - they've got permission to be there.
It's the first time ever that anyone other than MPs have been allowed to have a debate in the Commons chamber.
More than 300 of them packed into Parliament to talk about things including youth crime and the economy.
They also discussed free transport for children, lowering the voting age and whether university education should be free across the UK.
How does the Youth Parliament work?
MYPs are elected in annual youth elections across the UK
MYPs stand for Member of Youth Parliament
Anyone aged 11 to 18 is allowed to stand or vote
In the past two years, 1m young people have voted in elections
A few MPs were there to watch what was happening, and Commons Speaker John Bercow kept an eye on the rules.
When the kids entered the chamber he said: "Good morning and welcome. This is an historic occasion. It's one that we hope you will enjoy and all of us will treasure."