score:6
If you have a visa, it's either single-entry or multiple-entry. If you have visa-free entries, it works as if you were getting a new visa each time you cross the border. You can visit multiple times, as long as your total number of days of presence never goes beyond more than three months in a half-year.
Upvote:1
This site answer your question: http://www.lonelyplanet.com/thorntree/thread.jspa?threadID=1841750
Look:
The official rule for the Schengen visa is that, on the day you first enter any country within the Schengen zone, you start a 180 day "period", within which you can stay a maximum of 90 days in all Schengen countries. After you have racked up your 90 days (in one go, or in several chunks if you leave to non-Schengen countries & come back), you can't enter any Schengen country again until your 180 period ends. And on day 180, no matter what, you have to leave Schengen territory (even if you haven't used all your 90 days), but you can then turn around & come back in again the next day & get a new 90/180 day period. So: if you enter on day 1 & stay for 90 days immediately, you have to leave on day 90 & cannot re-enter any Schengen country until your 180 day "period" is up.
I hope this will be useful to you.