Greece, up to 3 years of Tax Treaty

3 years of teaching/research tax treaty with unlimited exemption

Tax treaty for Professors, Teachers, and Researchers

A professor or teacher who is a resident of Greece and who is temporarily in the United States to teach at a university, college, or other educational institution for a maximum of 3 years is exempt from U.S. income tax on the income received for teaching during that period.

(Reported from Internal Revenue Service (IRS), US government Publication 901)