There's going to be a big vote in the UK about the European Union.
It's called a referendum and everyone in Britain who is registered to vote can take part.
People will decide if they want to accept a new EU constitution, that's a set of rules about how the EU is run.
Why are the rules changing?
Most people agree that now the EU has grown from 15 to 25 members it has got too big to make decisions the way it used to.
This means the EU must get a new set of rules, or make fewer decisions. There have been a lot of arguments in the UK about whether any changes will be good for this country.
A referendum will let ordinary voters have their say.