If I travel from France to Switzerland, does the 3 month clock start again?

Hmm, yes, but hypothetically, one could enter Schengen for one day, leave, come back for 89 days to fulfil the 90/180 rule. What is unclear is that if it's possible to then directly start another 180 day period by staying 90 days more, making it 179 consecutive days. This started to bother me now, thanks to tony_b :-) I sent an email about this to the Finnish foreign ministry, let's see if they bother to put my bother to rest.

enter Schengen for one day, leave, come back

To be clear, leave for 89 days, and come back.

The sensible answer, in my mind, would be that it's 90 days out of any 180 days, however immigration decides to choose that 180 day period. But sensible and immigration/visa laws don't always go together.

Thanks for the correction. Yes, my example should have read as follows.

PERIOD 1
1 day in Schengen.
90 days out of Schengen.
89 days in Schengen again.

So now what happens if someone wants to start Period 2 starting with 90 days in Schengen? That would make 179 consecutive days in Schengen.

I think part of the difficulty lies in the fact that each member-state has its own immigration service and, presumably, its own interpretation of the rule. Therefore it seems to be impossible to come up with a concrete answer that applies to the whole of the Schengen Area.

However, I hasten to add that for the vast majority of visitors to Europe, this is not an issue at all. They come for a few days or 2 - 3 weeks and then go back home.

i think the issue has been discussed to death here and i thought had been answered- basically, if you answer 'yes' to the question: during the last 180 days, did you spend 90 days or less in Schengen' you're OK. It's a rolling 180 days.

OP, you're question is akin to a EU citizen asking if they get another 90 day visa waiver if they cross the state line from New York state into New Jersey and then return to New York state.

OP here,
Well, you guys certainly answered the question for me. I do appreciate it : )

you're welcome!

Well, the practice in #14 would be the one that makes sense. I, however, just received a reply from the Finnish foreign ministry, who forwarded a reply from the Finnish border guard, which says it's not a rolling 90/180. Instead, the first 180 day period starts when you first enter. Subsequent 180 day periods start the first time you re-enter after the end of the previous 180 day period. Thus, the following should be possible:

Day 1: Enter Schengen, see the cathedral, grab a beer, leave the same day
Days 2-91: Outside Schengen
Days 92-180: Inside Schengen 89 days, exit, 1st period ends
Day 181: Outside Schengen for 1 day (you have to to exit, according to the document)
Days 182-271: Enter Schengen, 2nd 180 day period starts, stay 90 days

So according to the rules (20th article of the Schengen general agreement, I was informed), an almost continuous 179 day stay is possible with perfect planning. Of course, trying to convince a random immigration officer about your cleverness might back-fire :-)

And just to add, I presented the hypothetical itinerary above to the Ministry, to be sure that I got it right, and almost immediately received a reply: "Yes, you understood correctly".

mpjohans, thanks for taking the trouble to do the research. All we need now is for someone to do the same with all the other 24 Schengen Area member states because I doubt that there is a consistent interpretation right across the board :-(