The United States is one of the very few countries, and the only major country, that taxes its citizens, no matter where they live. If you haven't lived in the United States in decades, you must pay tax on your worldwide income as if you never left. Even "accidental" U.S. citizens born overseas with at least one U.S. parent, who never set foot in the United States, must file U.S. tax returns. Beneficiaries of a deceased U.S. citizen living abroad must prepare a U.S. estate tax return and possibly pay estate tax, even if they're non-U.S. citizens who have never lived in the United States.