passport for France

It is not 3 months it is 90 days out of any 180 day period in the Schengen zone which includes France. Don't miscount. It cost one young lady $500 Euro for thinking 90 days meant 3 months. So if you are there 90 days then you have to wait 90 days to return.

"simple question with a simple answer" Really, Frank - you've personally tested the 90-days? I think I'd like to hear from the embassy/consulate, if you don't mind! It was a very simple question with a very simple answer. The Schengen agreement allows a US citizen to visit for up to 90 days within any 180 day period. Anything more requires a visa from that country where you wish to stay longer. Some countries might allow extended visa applications in-country, others do not. But the OP did not ask that.

I believe if you want to stay longer than 90 days, the visa to do so must be obtained in the U.S. before you go. You would do that through the French embassy. If all you had to do was go see the police after 90 days, a lot of people would do that. It's not up to the police how long someone stays. Why bother with that for an extra day or so? Just stay the 90 days.

Your 90 days begins when you arrive (if you're taking an overnight flight, the day you arrive is one day after the day your flight departs from the US) and ends on the day that you leave.

What Andrea said is correct. You may not change your visa status while you're in France.

France is not Germany just as Canada is not Argentina. All nations have their own laws. Schengen is only a limited scope agreement among nations.

You need to contact the consulate that covers your state, not the embassy in D.C. There are ten in the US. In France it's not so easy as in Germany. Before I was a dual citizen I once had to have permission for an extended stay with my French husband during a sabbatical. I had some sort of visa from the Consulate stating that I had to go to the Perfecture upon arrival. So, you make the appointment at the Prefecture of the Departement where you are staying. The backlog for an appointment can be up to a year, depending on the Departement.

I know everyone likes to expand the question, throw in their experience even if it doesn't relate, discuss unique situations, etc., but the OP was a very simple question with a simple answer. Ninety days in and ninety days out.

Lol. Yes, totally beyond his original question, like a game of telephone. In any case due to the above info about Germany, I do think it is necessary to clarify that it's not so simple in France. People reading the thread could be misled.