Many European countries (the Schengen states) require that your passport be valid for at least three months beyond your planned date of departure from the Schengen area.
Under the new system, you, as an EU, EEA or Swiss citizen, can continue to visit the UK without applying for a visa and in most cases, can stay for up to six months.
U.S. nationals, including U.S. dual nationals, must use a U.S. passport to enter and leave the United States. U.S. dual nationals may also be required by the country of their foreign nationality to use that country's passport to enter and leave that country.
In Asia, nations like China, Vietnam, Malaysia and Thailand enforce this rule. South American countries like Brazil, Venezuela and Bolivia also need a passport that's good for six months.
Can I Travel If My Passport Expires in Less Than Six Months? In normal circumstances, you can't travel with a passport that expires in less than six months. However, a country with an active agreement with your destination country may allow it.
The six-month passport validity requirement does NOT apply to an American citizen using a U.S. passport to enter Canada. He/she may do so up until the date of expiration of the passport.
For entry into Greece, your passport should have at least six months of remaining validity. While Greek law requires three months of passport validity beyond the intended date of your departure, if you are transiting a country that requires six months of validity, you may not be permitted to continue your trip.