There are a number of tax agreements that may affect the taxes of an expatriate. Some of these are host country specific. Always check the country you live in to check tax status.
U.S. tax treaties or conventions with many foreign countries entitle U.S. residents to certain credits, deductions, exemptions and reduced foreign tax rates. This is a way to pay less tax to those host countries. For example, most tax treaties allow U.S. residents to exempt part or all of their income for personal services from the treaty (host) country's income tax if they are in the treaty country for a limited number of days.