In practice, the US has lots of bilateral income tax treaties [1] that prevent expats' getting doubly taxed. For example, I'm an American living in London but

In practice, the US has lots of bilateral income tax treaties [1] that prevent expats' getting doubly taxed. For example, I'm an American living in London but I don't pay US taxes for work done here because the tax rate is higher here and by treaty, the UK gets first crack at me. I know a few Americans in (low-tax) Singapore who have to pay Singapore taxes, then pay the on top of that to the US government up to the level they would have been taxed if living in the US. I get extra pain when I go on business trips to the states, which the US doesn't count as being foreign work. So every year I have to fill in a spreadsheet of all the days I worked in each country, and subtract the US days from my tax treaty credits. I have to do the same thing in reverse for the HMRC in the UK. My least favorite part of being an expat :) [1] http://www.rumbaklaw.com/resources-and-tools/us-federal-tax-resources/countries-with-and-without-income-tax-treaties-with-the-u-s/ http://www.rumbaklaw.com/resources-and-tools/us-federal-tax-...