The French people have rejected plans for the European Union to have a new constitution in a key public vote.
Nearly 55% of the people who voted said they did not agree with the plans.
This result is really important because all 25 countries in the EU have to agree to the constitution changes if it is ever going to become law.
Some people want to change the constitution so that there is a clear set of rules which all member countries have to agree to accept.
However, the set of rules will only become law if all 25 members agree to it by the end of October 2006.
The French vote is a serious setback to the people who want the constitution changed.
All countries will have to say whether or not they agree with it before the 2006 cut off date.
British Prime Minister Tony Blair said it was too early to say whether there would be a public vote in Britain on this subject.