For residents of the USA, Canada, or any EU country who will be staying in France for less than 90 days, a valid passport is all you need.  If you want to stay longer than that, US and Canadian residents need to apply for a visa.  For more information about visas and customs, you can go to the official site of the French Tourism Office: us.franceguide.com/

 EU residents have the right to stay and work in any other EU nation. Technically, an EU resident staying in France for more than 90 days is supposed to apply for a carte de séjour. If you cross the border into another EU nation and then return, you can stay for another 90 days without applying.