This page contains information about data sources and limitations for SOI's nonresident alien tax study. Please visit Nonresident Alien Estate Tax Statistics to access articles and tables from the study. Since 1995, SOI has conducted an annual study of Federal estate tax returns filed for nonresident aliens (Forms 706-NA). Demographic, financial and asset information were extracted from the population of Form 706-NA filers. No amounts shown are estimates, rather, they are pre-audit population figures. The United States maintains estate and gift tax treaties with a variety of countries to minimize double taxation. Because the tax law applicable to decedents domiciled in and/or a citizen of treaty countries varies so greatly from the general population of nonresident alien decedents, the data from those Forms 706-NA explicitly recognized as being treaty returns are separated from the data from regular returns.