Documents needed when entering France to immigration
Whether or not you are required to obtain a visa before travelling, even if you are a US citizen, you may be requested to show the following elements to the French immigration officers upon arrival :
A valid passport (still valid 3 months after your expected return from France)
Means of support during the stay (cash, credit cards, traveler cheques…)
Accommodation reservations or an "attestation d’accueil"
A return plane ticket (for a short stay only),