France and Italy are signatories of the Schengen Agreement. Among other things, that means you go through immigration and customs once. You will go through immigration in Paris, but not in Florence. You will go through customs in Florence, but not in Paris.

Technically, you do not go through "Customs" in the traditional sense when traveling between France and Italy because both are members of the Schengen Area and the EU Single Market. However, in 2026, travelers frequently encounter "Internal Border Checks." Due to ongoing security concerns and migration pressures, France has extended its right to perform random ID and document inspections at land, air, and sea borders until at least April 30, 2026. This means that if you are taking the train from Nice to Ventimiglia or driving through the Mont Blanc Tunnel, you may be stopped by French or Italian police to show your passport or national ID card. While there are no duties to pay on personal goods, these security checkpoints can add 20 to 45 minutes of delay to your journey. Always have your travel documents accessible, as the "frictionless" border of the past has been temporarily replaced by a more scrutinizing, security-focused environment.