The United States has over 50 tax treaties with different countries. Although there are fundamental similarities among them, the treaties vary in significant ways in terms of the benefits they offer to students, the types of income covered, the total amount of the exemption, and the number of years one can claim the benefit. Although some treaties exempt 100 percent of some types of income, most treaties exclude only a portion of students' earnings, including assistantships. The university withholds tax on your earnings unless you make a claim for exemption by treaty.

Countries with which the United States has tax treaties are listed in IRS Publication 901 (PDF), U.S. Tax Treaties. Existence of a tax treaty does not automatically mean that a citizen of that country does not have to pay taxes.