Sanctuary, or asylum, is a very old legal concept that refers to the protection that a country or other sovereign provides to a national of another country fleeing war or persecution. Unlike most of US immigration law, asylum is unique in that it is derived from international law, including the 1951 United Nations Convention Relating to the Status of Refugees (Refugee Convention), which provides a definition of refugee and sets forth the principle of non-refoulement. Under the refugee convention and US asylum law, a refugee is a person who “owing to a well-founded fear of being persecuted for reasons of race, religion, nationality, membership of a particular social group or political opinion, is outside the country of his nationality and is unable or, owing to such fear, is unwilling to avail himself of the protection of that country.”

The principle of non-refoulement is the principle that a country may not return a refugee to countries where they would face persecution based on one of these protected grounds. Another international treaty is the Convention Against Torture and Other Cruel, Inhuman and Degrading Treatment or Punishment (CAT), to which the US is also a signatory, that prohibits returning a person to a country where there are “substantial grounds for believing that he would be in danger of being subjected to torture.”