For the last several years, Central American migrant families have arrived at the U.S.-Mexico border in relatively large numbers, many seeking asylum. While some request asylum at U.S. ports of entry, others do so after entering the United States "without inspection" (i.e., illegally) between U.S. ports of entry. On May 7, 2018, the Department of Justice (DOJ) implemented a zero tolerance policy toward illegal border crossing both to discourage illegal migration into the United States and to reduce the burden of processing asylum claims that Administration officials contend are often fraudulent. Under the zero tolerance policy, DOJ prosecutes all adult aliens apprehended crossing the border illegally, with no exception for asylum seekers or those with minor children. DOJ's policy represents a change in the level of enforcement for an existing statute rather than a change in statute or regulation. Prior Administrations prosecuted illegal border crossings relatively infrequently. Criminally prosecuting adults for illegal border crossing requires detaining them in federal criminal facilities where children are not permitted. While DOJ and the Department of Homeland Security (DHS) have broad statutory authority to detain adult aliens, children must be detained according to guidelines established in the Flores Settlement Agreement (FSA), the Homeland Security Act of 2002, and the Trafficking Victims Protection Reauthorization Act of 2008. A 2015 judicial ruling held that children remain in family immigration detention for no more than 20 days. If parents cannot be released with them, children are treated as unaccompanied alien children and transferred to the Department of Health and Human Services' (HHS's) Office of Refugee Resettlement (ORR) for care and custody. The widely publicized family separations are a consequence of the Trump Administration's 100% prosecution policy, not the result of any family separation policy. Following mostly critical public reaction, President Trump ordered DHS to maintain custody of alien families during the pendency of any criminal trial or immigration proceedings. DHS Customs and Border Protection (CBP) subsequently stopped referring most illegal border crossers to DOJ for criminal prosecution. A federal judge then mandated that all separated children be promptly reunited with their families. Another rejected DOJ's request to modify the FSA to extend the 20-day child detention guideline. DHS has since reverted to some prior immigration enforcement policies. Family unit apprehensions, which increased from just over 11,000 in FY2012 to 68,560 in the first nine months of FY2018, are occurring within relatively low historical levels of total alien apprehensions. The national origin of recently apprehended aliens and families has shifted from mostly Mexican to mostly Central American. Administration officials and immigration enforcement advocates argue that measures like the zero tolerance policy are necessary to discourage migrants from coming to the United States and submitting fraudulent asylum requests. They maintain that alien family separation resulting from the prosecution of illegal border crossers mirrors that occurring under the U.S. criminal justice system policy where adults with custody of minor children are charged with a crime and held in jail, effectively separating them from their children. Immigrant advocates contend that migrant families are fleeing legitimate threats from countries with exceptionally high rates of gang violence, and that family separations resulting from the zero tolerance policy are cruel and violate fundamental human rights-such as the ability to request asylum. Some observers question the Trump Administration's capacity to marshal sufficient resources to prosecute all illegal border crossers without additional resources. Others criticize the family separation policy in light of less expensive alternatives to detention.