Visits to the "Schengen" group of countries are limited to 90 days in six months for U.S. citizens. With electronic scanning of passports, the media report that the limit is being enforced.
"You can only stay for three months in the Schengen area within a six month
period. The Schengen area comprises of Austria, Finland, Greece,
Luxembourg, Portugal, Belgium, France, Iceland, Netherlands, Spain, Denmark,
Germany, Italy, Norway and Sweden.
[For example] If you already stayed in Holland for three months, you would now have to
stay outside of the Schengen area for three months before you can enter for
a further three months.
The alternative to this would have been to apply for a visa for a longer
period for the Schengen area in the U.S. before you left."
It is hard to leave the rat race behind!