All countries reserve the right to deport persons without right of abode even those who are longtime residents or possess permanent residency. In general, foreigners who have committed serious crimes, entered the country illegally, overstayed or broken the conditions of their visa, or otherwise lost their legal status to remain in the country may be administratively removed or deported. In some cases, even citizens can be deported; some of the countries in the Persian Gulf have deported their own citizens. They have paid the Comoros Islands to give them passports and accept them.
 Some western countries also have the ability to deport citizens, if they have another nationality or if they acquire citizenship through fraud.
In many cases, deportation is done by the government's executive apparatus, and as such is often subject to a simpler legal process (or none), with reduced or no right to trial, legal representation or appeal due to the subject's lack of citizenship. For example, in the 1930s, during the Great Depression, more stringent enforcement of immigration laws were ordered by the executive branch of the U.S. government, which led to the expulsion of up to 2 million Mexican nationals from the United States. In 1954, the executive branch of the U.S. government implemented Operation Wetback, a program created in response to public hysteria about immigration and immigrants from Mexico. Operation Wetback led to the deportation of nearly 1.3 million Mexicans from the United States. Between 2009 and 2016, about 3.2 million people were deported from the United States. Since 1997 U.S. mass deportations of non-citizens particularly convicted felons have risen steadily with the passing into law by the U.S. Congress of the 1996 Illegal Immigration Reform and Responsibility Act (IIRRA) which brought sweeping changes to the threshold for deportation of convicted felons that have been criticized by some as having human rights abuses. Since this time, the former U.S. Immigration and Naturalization Services (INS) has been transformed into Immigration and Customs Enforcement (ICE) and has renamed deportation as "expedited removal". The ICE website publishes removal statistics annually on its website. According to recent numbers ICE removed a total of 240,255 aliens in FY 2016, a two percent increase over FY 2015, but a 24 percent decrease from FY 2014.
Already in natural law of the 18th century, philosophers agreed that expulsion of a nation from the territory that it historically inhabits is not allowable. In the late 20th century, the United Nations drafted a code related to crimes against humanity; Article 18 of the Draft Code of Crimes Against the Peace and Security of Mankind declares "large scale" arbitrary or forcible deportation to be a crime against humanity.
Deportation often requires a specific process that must be validated by a court or senior government official. It should not be confused with administrative removal, which is the process of a country denying entry to individuals at a port of entry and expelling them.