Schengen

Schengen is a small town in Luxembourg near the French and Dutch borders. Back in 1985, Luxembourg, the Netherlands, France, Belgium and West Germany signed the Schengen Agreement which called for the gradual removal or checks at their common borders.

Since then 25 countries have joined the Schengen zone. They are Austria, Belgium, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Slovakia, Slovenia, Spain, Sweden and Switzerland. Romania and Bulgaria hope to join later in 2011.  San Marino, Vatican City and Monaco are all de facto members.

Schengen is different from the EU. Iceland, Norway and Switzerland are not members of the EU but are part of the Schengen zone. Ireland and the United Kingdom are EU members but are not Schengen members.  They have their own Common Travel Agreement.

There are no passport checks when traveling between Schengen countries. I don't get a passport stamp when I travel from Czech Republic to Germany. However, I do get stamped coming and going between Germany and the UK because the UK isn't a Schengen country.

USA citizens don't need a visa to enter the Schengen zone. But there is a maximum stay of up to 90 days in a six-month period. Overstaying the 90 days is a big deal. There is a very hefty fine, you get deported and are banned from entering any Schengen country from 1 to 5 years. They don't play around with this over here.

One of the reasons my long-term visa (green card) is so complicated is because the Czech Republic is now part of Schengen. The visa allows me to reside full-time (for 1 or 2 years) in the Czech Republic and allows me to travel within all of the other Schengen countries without border checks.

Update: In December 2011, Switzerland and Liechtenstein both joined Schengen.  

Update: As of January 2016, Bulgaria and Romania are still not yet members.  No word yet either on when Cyprus will join.

Update: Croatia joined the EU in 2013 and should have joined Schengen by 2015.  It is on track now to join in 2020.

Update 2023:  Croatia joined Schengen but Bulgaria and Romania still haven't joined.