US residents who are not citizens of the United States face different estate tax rules depending on whether they qualify as US domiciliaries.

According to the IRS, those persons are considered to be domiciled in the United States who live here with no definite present intent to move abroad. Even if such an intent is formed after having moved here with no definite intent to move, it does not matter unless the person actually moves abroad.

US domiciliaries enjoy the high federal estate tax exemption amount of currently USD 5.49 million. Their worldwide assets are subject to US federal estate tax.

Non-US domiciliaries have a federal estate tax amount of only USD 60’000.

Keep in mind that the IRS defines US residents differently for income and estate tax purposes. Even if you are not required to pay federal income taxes (for example because you are a non-US citizen who works at the World Bank, the International Monetary Fund or other international organization), you can still be considered a US domiciliary.

The opposite is also true. US permanent resident (green card holder) status does not necessarily mean that you are a US domiciliary. Say that you are a Canadian citizen, your main home and assets are in Canada, but you have acquired the permanent resident status to spend time at your vacation home in Florida. You are not a US domiciliary for estate tax purposes.