Americans abroad face special tax issues since, unlike many countries, the U.S. taxes all of a citizen's income, whether earned in the U.S. or not. Income earned while living overseas could be taxed by both the U.S. and a host country.
Each country has unique rules. In Argentina, there's no capital-gains tax, but there is a 0.5 percent to 1.5 percent tax on net worth, and residents are taxed on worldwide income. Because of that, the Weldons haven't become official residents of Argentina. They leave every 90 days, often for a day trip to Uruguay.
There are tax treaties and special provisions that can reduce tax burdens on expatriates. Unfortunately it takes a tax specialist to navigate them.
Photograph by Diego Giudice/Bloomberg