Prime Minister Tony Blair has said he wants to hold a referendum on whether or not the European Union should have a constitution, which is causing a big fuss among MPs.
Our Man in Parliament gives us the lowdown on what this all means.
What exactly is Tony Blair announcing today?
He wants to hold a referendum on the European constitution.
What does that mean?
He wants to organise a big public vote, like a general election, so everyone in the country - over the age of 18 - can have a say on whether they want Britain to sign up to a constitution for Europe.
What is a constitution anyway?
It's basically a rule book. Most clubs have them - and many countries.
So what is all the fuss about?
The European Union already has its own flag, anthem and parliament..
Many people are worried that if it gets a constitution as well it will become a country in all but name - a United States of Europe.
According to opponents of a constitution that means important decisions on things like the economy and defence will no longer be taken by MPs elected by the British public but by bureaucrats in Brussels.
What does Tony Blair think?
He says the European Union can not expand to become a club of 25 countries without having a proper set of rules written down. Without it, there will be chaos, he argues.
He believes the advantages of being in Europe - in terms of jobs and prosperity - far outweigh any problems caused by signing up to a joint set of rules.
And he has promised not to give away Britain's powers in areas such as defence, the economy and law.
Why bother holding a referendum, then?
Up until this week, Mr Blair had always said he did not think it was worth it.
So why has he changed his mind?
He has given in to pressure from the Conservatives, Liberal Democrats and a growing number of his own MPs, who all believe the constitution is important enough for the public to be given a say.