U.S. Citizens and Resident Aliens Abroad (from IRS website)

Filing Requirements
If you are a U.S. citizen or resident alien living or traveling outside the United States, you generally are required to file income tax returns, estate tax returns, and gift tax returns and pay estimated tax in the same way as those residing in the United States.

Foreign Earned Income Exclusion
To claim the foreign earned income exclusion, the foreign housing exclusion, or the foreign housing deduction, you must have foreign earned income.
Foreign earned income generally is income you receive for services you perform during a period in which you meet both of the following requirements.

•  Your tax home is in a foreign country.
•  You meet either the bona fide residence test or the physical presence test.