An expatriation tax or emigration tax is a tax on persons who cease to be tax resident in a country. This often takes the form of a capital gains tax against unrealised gain attributable to the period in which the taxpayer was a tax resident of the country in question. In most cases, expatriation tax is assessed upon change of domicile or habitual residence; in the United States, which is one of only three countries (Eritrea and Myanmar are the others) to substantively tax its overseas citizens, the tax is applied upon relinquishment of American citizenship, on top of all taxes previously paid.