A referendum on the Treaty establishing a Constitution for Europe was held in France on 29 May 2005 to decide whether the French government should ratify the proposed constitution of the European Union. The result was a victory for the "no" campaign, with 55% of voters rejecting the treaty on a turnout of 69%.

The Treaty establishing a Constitution for Europe was an unratified international treaty intended to create a consolidated constitution for the European Union (EU). It would have replaced the existing European Union treaties with a single text, given legal force to the Charter of Fundamental Rights, and expanded qualified majority voting into policy areas which had previously been decided by unanimity among member states.