U.S. and Canadian citizens do not need visas to enter France for short visits of up to 90 days. The exceptions to that rule are for journalists traveling to France on assignment, crew members on short-term assignment (film crews, etc.) and individuals holding diplomatic or official passports, all of whom will need to submit a short-stay visa application to the French embassy or consulate closest to you.
France is one of 15 countries belonging to the Schengen territory, which means U.S. and Canadian passport holders may transit into France through any of the following countries without a visa:

Also note that U.S. and Canadian citizens do not need visas to transit from French airports to non-Schengen territory countries. However, be sure to verify the visa requirements for the country you will be heading to from France.

European Union members do not require visas to enter France, and may stay in France without limitation.  

All other nationalities can find visa information on this French consulate page.