It is best to have at least 6 months after your date of return to the US remaining on your passport.
Yes, you will need a passport at each end of the journey.
None needed for travel within US
For the EU citizen, to travel inside EU (like from Ireland to Poland) a valid ID is required, but not necessary a passport.
Citizens of the European Union (both the UK and Portugal are members) can travel inside the Union for unlimited period of time without a visa and validity of less than 6 months is not an issue.
Since Ireland and Portugal are both members of the European Union, they no longer require passports for travellers between those two countries. If, however, you happen to be a visitor from the US who is presently in Ireland but planning to visit Portugal, then you still need a passport, and you should not try to travel on an expired passport. Visit the American embassy and renew your passport.
How long needed on passport to travel to FinlandFinland
As long as your are travelling outside of the Unoted States boarder, then you do need a passport.
UK passport holders require 6 months left on their passport
Yes, you need a passport to travel to Europe.
Yes, you need a passport to travel to Paris.
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You don't need a passport to travel between the UK and the Republic of Ireland.
No. As long as you are traveling to or from other US States you do not need to bring your passport
You need a passport
No, you do not need a passport to travel to Arizona if you are a U.S. citizen.
Yes, you need a valid passport to travel to Brazil.
Yes, you need a valid passport to travel to Colombia.