When a non-U.S. national (alien) enters the United States illegally or overstays a temporary visa, her presence in the country violates the Immigration and Nationality Act (INA). She is subject to removal from the country on that basis alone, regardless of whether she has a criminal history or other factors, and there are few circumstances in which she can legalize her presence to extinguish the statutory basis for her removal. The population of aliens in this situationâthat is, aliens whose presence in the United States violates the INA, referred to here as "unlawfully present aliens" âcurrently numbers between ten million and twelve million, according to some recent estimates. About 80% of unlawfully present aliens have been in the United States for more than ten years, according to a study by the Department of Homeland Security (DHS). The issue of whether and to what extent to legalize or provide other relief from removal to unlawfully present aliens is a frequent topic of debate in Congress. The issue is sometimes called the "third leg of the stool" of immigration reform, after the issues of border enforcement and legal admissions. Many (but not all) proposals for comprehensive immigration reform include provisions that would create pathways to lawful permanent residence for unlawfully present aliens in significant numbers. These bills generally follow a model for one-time legalization programs exemplified by the Immigration Reform and Control Act of 1986, which offered the prospect of lawful permanent resident (LPR) status to much of the unlawfully present population in the United States at that time. Other bills would create legalization programs for discrete segments of the unlawfully present population; the various Dream Act proposals, for example, would offer relief to many childhood arrivals. These legislative proposals contemplate ad hoc legalization measures: they would offer relief to extant populations of unlawfully present aliens, but the proposals would not change generally applicable law concerning legalization going forward. The version of the DREAM Act recently passed by the House of Representatives, for example, would create a pathway to LPR status for some unlawfully present childhood arrivals who entered the United States at least four years before enactment; the bill would not, however, change the INA's approach to future childhood arrivals. This report covers the current law that underlies the ad hoc legalization debate. It reviews the limited extent to which, under the INA, an unlawfully present alien can obtain a legal immigration status that extinguishes the statutory basis for removal. In other words, the report explains the narrow circumstances in which unlawfully present aliens can legalize under current law. As used here, "legalization" means the acquisition of a lawful immigration status by an unlawfully present alien so that he or she is no longer subject to removal under the INA. Because the INA takes a restrictive approach to legalization, the term is often used synonymously with ad hoc legalization to refer to proposals for programs of one-time relief. This report, in contrast, focuses on legalization under current law. To the exclusion of other issues, this report focuses on the circumstances in which the INA allows acquisition of legal status notwithstanding unlawful presence. Many of the statutory provisions discussed that allow legalization in limited circumstancesâsuch as adjustment of status, asylum, and cancellation of removalâapply to lawfully present aliens as well, but those aspects of the statutes are not explored here. Further, most of the statutory provisions treated here have requirements that disqualify aliens with certain criminal convictions or immigration violations. Those requirements are referenced but not analyzed here; another CRS report discusses them in more depth. The INA takes three primary approaches to regulating the unlawfully present population: removal, deterrence, andâto a lesser extentâlegalization. First, unlawfully present aliens are subject to removal for as long their presence violates the INA; no statute of limitations applies. This regime of perpetual removability has been a feature of U.S. immigration law since 1924. Under it, aliens who enter the country surreptitiously or overstay nonimmigrant visas may be removed even after many years in the United States, whether or not they have committed other crimes or offenses. Enforcement of this legal regime comes with a well-known catch: the federal government does not allocate enough resources to make the removal of all unlawfully present aliens possible. According to DHS estimates and removal statistics, the agency's resources allow it to pursue removal each year of only a small fraction of the approximately ten million to twelve million unlawfully present aliens in the United States. There is an enforcement gap, in other words. In response, executive branch administrations have, to varying degrees, established enforcement priorities to focus their removal resources on aliens who have committed crimes or who meet other criteria. But the point remains that unlawfully present aliens face perpetual risk of removal under the INA, even if only a small percentage are actually placed in removal proceedings each year. Second, the INA seeks to deter the arrival or continued presence of unlawfully present aliens. It criminalizes some immigration violations, such as illegal entry and reentry, and bars most aliens who lack lawful immigration status from working or receiving federal public benefits. The INA renders aliens who commit some immigration violations inadmissible (i.e., ineligible for admission), either for a specified time period or for life. Aliens who are unlawfully present in the United States for one year or more, for example, are inadmissible for ten years once they depart, subject to some waiver provisions. Aliens who reenter the country illegally after being removed are inadmissible for life, also subject to limited waiver. Finally, legalization: as this report explains, the INA offers limited opportunities for unlawfully present aliens to acquire legal immigration status that extinguishes the statutory basis for their removal. An alien who overstays a nonimmigrant visa and later marries a U.S. citizen (or otherwise becomes the immediate relative of a U.S. citizen) can legalize through the adjustment of status process, so long as he or she has not committed certain crimes and does not fall within other eligibility bars. Beyond that notable exception, the legalization mechanisms in the INA exist mainly to relieve specific types of hardships such as persecution abroad (asylum) or the extreme hardship that U.S. citizens or LPRs would suffer due to the removal of their parents (cancellation of removal). Where these forms of relief do not apply, unlawfully present aliens may seek to legalize by leaving the country and applying for an immigrant visa abroad on the basis of a qualifying family relationship or in an employment or diversity category. In most cases, however, their prior unlawful presence in the United States will make them ineligible to return for ten years. As such, under current law, it is generally more difficult for unlawfully present aliens in the United States to obtain legal immigration status on generally applicable grounds, such as qualifying family relationships, than it is for aliens abroad applying to immigrate on the same grounds. U.S. immigration law developed its current stance toward the unlawfully present population in the middle period of the twentieth century, when Congress strengthened removal statutes and allowed the primary legalization statuteâknown as the registry statute, which provided for legalization based on long-standing presenceâto become obsolete. Illegal immigration emerged as a significant issue in the United States with the advent of quantitative immigration restrictions in the 1920s. Until 1875, the only restrictions on immigration into the United States came from state laws providing for the exclusion or expulsion of convicts, paupers, and people with contagious diseases. The Page Act of 1875 imposed the first federal restrictions when it barred convicts and prostitutes. Additional qualitative restrictions, including bars against Chinese laborers and aliens "likely to become public charges," followed in the ensuing decades, culminating in the imposition of a literacy test in 1917. The first numerical restrictions on immigration were not imposed until 1921, when the temporary measures of the Emergency Quota Act capped new admissions by nationality (at 3% of the foreign-born population of each nationality, as reflected in the census of 1910). Congress established a permanent and generally more restrictive system of national origins quotas in the Immigration Act of 1924, also known as the Johnson-Reed Act. Numerical limitations of some form have remained a fixture of U.S. immigration law ever since. Some illegal immigration had existed during the regime of qualitative restrictions that began in 1875, but it increased with the introduction of numerical caps. The 1924 Act, beyond establishing a permanent quota system, was also notable for its removal provisions. The act rendered aliens who entered or remained in the country in violation of its restrictions subject to deportation "at any time after entering," which meant that no limitations period applied and even long-standing unlawfully present aliens could be deported. This marked a significant change from earlier deportation statutes, which had imposed limitations periods of between one and five years for the removal of illegal entrants. Aliens physically present for longer than the limitations period could not be deported under those laws on the ground that their presence violated the immigration statutes. The 1924 Act eliminated this limitations period going forward. Yet soon after U.S. immigration law settled upon this regime of perpetual deportability of unlawfully present aliens, the law also developed a mechanism called "registry" for such aliens to legalize on the basis of long-standing presence. Congress enacted the first registry statute in 1929 and revised it periodically thereafter. Generally speaking, the registry statute authorized immigration officials to grant lawful permanent residence to aliens who entered the United States before a date specified in the statute and who resided in the country continuously after entry. To qualify, aliens also had to demonstrate "good moral character" and not be ineligible on certain grounds that changed over time (e.g., not have certain criminal convictions). Unlawful presenceâwhether as a result of surreptitious entry or the overstay of a visaâwas not a bar to registry. In plain terms, then, the registry statute provided for the legalization of unlawfully present aliens who had been in the United States since a given cutoff date. The first cutoff date, under the 1929 statute, was June 3, 1921. Congress apparently sought to provide relief to aliens who entered the United States before the first numerical restrictions went into effect in 1921 and before immigration officials began systematically recording alien admissions at ports of entry. In 1939, Congress advanced the cutoff date to 1924. About 200,000 aliens appear to have legalized through registry between 1929 and 1945. A few more changes to the cutoff date followed in later decades. A 1958 law advanced the date from 1924 to 1940; a 1965 law moved it up to 1948; and in 1986, the Immigration Reform and Control Act (IRCA) set the current date of 1972. Under current law, the registry statute remains in effect, but the 1972 cutoff date renders it mostly obsolete. Registry applications surged on the heels of the 1986 update that set the date at 1972, but applications dwindled to a trickle as the date grew more distant. In 2004, the last year for which DHS published separate statistics on registry in its statistical yearbook, 205 aliens became LPRs through registry. Thus, while the concept of registry persists in U.S. law as a legalization mechanism based on long-standing presence, few (if any) unlawfully present aliens qualify to legalize through registry because few have been present since the 1972 cut-off date. Perhaps the most significant body of legalization principles in the INA governs the extent to which unlawful presence disqualifies an alien from obtaining LPR status through family relationships or on other generally applicable grounds. With the registry statute effectively obsolete, federal law no longer provides for the legalization of unlawfully present aliens based on the duration of their presence in the country alone. But unlawfully present aliens often come within the generally applicable criteria that the law uses to select aliens for immigration to the United States. The INA allocates immigrant visas to three major categories of aliens: family-based immigrants, employment-based immigrants, and diversity-based immigrants. Family-based immigrants account for about two-thirds of permanent immigration to the United States each year; employment-based immigrants account for about 12%; and diversity-based immigrants account for about 4% (refugees, asylees, and some other categories account for the remainder). An unlawfully present alien would come within one of these categories, to give some examples, by marrying a U.S. citizen, having a U.S. citizen son or daughter who turns twenty-one, obtaining an offer of employment that qualifies for an employment-based immigrant visa, or entering and winning a visa slot in the diversity lottery program. The law's approach to aliens in this situationâthat is, aliens who become eligible for an immigrant visa while living in the United States in violation of the INAâis to impose two interlinking obstacles to their acquisition of LPR status. First , current law prohibits most (but not all) such aliens from obtaining LPR status unless they depart the United States to apply for the immigrant visa at a U.S. consulate abroad. As discussed below, exceptions to this prohibition allow some groups of unlawfully present aliens who are eligible for immigrant visas to become LPRs by adjusting their status from within the United States. The most notable exception benefits those aliens who enter on a nonimmigrant visa, overstay, and then marry a U.S. citizen or otherwise become the immediate relative of a U.S. citizen. Second , most unlawfully present aliens who depart the United States to apply for immigrant visas abroad will face a bar on readmission of three years from the date of their departure (for aliens unlawfully present for more than 180 days) or ten years from the date of their departure (for aliens unlawfully present for one year or more). Unless they receive a discretionary waiver of the ineligibilityâa remedy with narrow eligibility criteriaâthey generally must wait out the bars abroad. In general, then, the INA imposes a double barrier to the legalization of unlawfully present aliens who come within an immigrant visa category: the law prohibits such aliens from seeking LPR status unless they apply from abroad (the first barrier) and then bars their readmission for three or ten years once they depart the United States (the second barrier). Crucially, the three- and ten-year bars on readmission apply only if the alien departs the United States following the period of unlawful presence. The law that governs an alien's eligibility to adjust status from within the United Statesâthat is, to obtain LPR status without departingâis therefore hugely important, because in most cases it determines whether an unlawfully present alien in an immigrant visa category must face the three- and ten-year bars before obtaining legal status. In many cases, a grant of advance paroleâessentially, an assurance from DHS that it will allow an alien to reenter the country on immigration parole after a trip abroadâcan help an unlawfully present alien become eligible to adjust status, as discussed further below. Adjustment of status under INA Â§ 245 is the legal mechanism that makes it possible for an alien who is present in the United States and qualifies for an immediately available immigrant visa to acquire LPR status without leaving the country. Like most immigration benefits, adjustment of status is a discretionary remedy: the INA authorizes but does not require immigration authorities to grant it to eligible aliens. This mechanism did not exist in federal immigration statute until 1952. Its inexistence before that date sometimes forced creative administrative maneuverings. In the early 1940s, people fleeing German-occupied Europe who entered the United States on temporary visas or on immigration parole, and who qualified for and had the government's support to acquire LPR status, could gain such status only by departing the country to apply for U.S. immigrant visas. A special arrangement between the U.S. and Canadian governments facilitated such persons' entry into Canada to apply for the visas at the U.S. embassy there, with the understanding that they would return to the United States as LPRs. In 1945, President Truman issued a presidential declaration to exempt from this exit-to-enter procedureâwhich he considered "wasteful"âa group of about 1,000 displaced persons who had been brought from camps in Italy to a War Relocation Camp near Oswego, New York. The first version of the adjustment of status statute was enacted seven years later. Under current law, an alien seeking to adjust to LPR status within the United States must meet several requirements, two of which have outsize implications for the unlawfully present population: (1) the alien must have been "inspected and admitted or paroled into theÂ  United States ," and (2) the alien must have maintained "lawful status," including by not accepting unlawful employment after entry. Accordingly, aliens who entered the United States surreptitiously generally cannot adjust status, because they were neither "inspected and admitted" nor "paroled" into the United States, and also because they have not maintained lawful status after entry. Similarly, aliens present in the United States after overstaying their nonimmigrant status generally cannot adjust: although they were "inspected and admitted," they failed to maintain lawful status by overstaying. Exceptions exist to both requirements, however, as do administrative procedures that provide relief from them, as explained below. Perhaps most notably, the second requirementâmaintenance of lawful statusâdoes not apply to the immediate relatives of U.S. citizens. One significant statutory provisionâINA Â§ 245(i)âchanged the adjustment of status framework by lifting the lawful entry and maintenance of status requirements for aliens eligible for family-based or employment-based immigrant visas, provided they paid a $1,000 fine and met certain other requirements. INA Â§ 245(i) thus cleared the way for many unlawfully present aliens, including unlawful entrants, to adjust status. However, the provision has a cutoff dateâit applies only to aliens for whom a visa petition or application for labor certification was submitted before April 30, 2001âthat makes it inapplicable to most cases today. Accordingly, under current law, aliens generally may adjust status only if they meet the lawful entry and maintenance of status requirements or fall within an exception to those requirements. Exceptions to the lawful entry requirement (i.e., the requirement that an alien must have been "inspected and admitted or paroled" in order to adjust status) exist for victims of domestic violence, certain statutorily defined "special immigrants" who are juveniles or have affiliations with the U.S. Armed Forces, and aliens who meet the INA Â§ 245(i) cutoff date. To illustrate with a domestic violence example, if an alien enters surreptitiously and suffers domestic violence in the United States at the hands of an immediate relative who is a U.S. citizen or LPR, the alien may apply to adjust status notwithstanding the surreptitious entry. Some (but not all) federal courts have held that aliens who acquire Temporary Protected Status (TPS) meet the lawful entry requirement, even if they are present in the United States following a surreptitious entry. Where none of these narrowly drawn exceptions applies, however, a grant of immigration parole from DHS can enable an alien who entered the country surreptitiously to adjust status. In other words, a grant of parole can function as a work-around for the bar that unlawful entry typically poses to adjustment of status. This is because, even if the alien was not "inspected and admitted," the alien can qualify to adjust status by being "paroled." DHS most commonly exercises the parole power to permit entry to aliens not yet on U.S. territory who are (or may be) inadmissible. In some circumstances, however, DHS also grants parole to unlawfully present aliens. Grants of parole to aliens physically present in the U.S. come in two forms: (1) "parole in place," which confers parole status on physically present aliens without requiring them to leave and come back; and (2) "advance parole," which allows unlawfully present aliens to depart the United States with an assurance that they will be permitted to reenter on parole. Both varieties of parole satisfy the lawful entry requirement for adjustment of status, even when granted to an alien present following a surreptitious entry, although for advance parole the alien must actually leave and be paroled back into the country. The eligibility criteria for both of these parole programs are set by DHS and recorded in internal memoranda and agency manuals; no statute or regulation spells out which aliens may qualify for parole in place or advance parole. Accordingly, it can sometimes be difficult to track DHS's practice in granting these forms of relief. The agency appears, however, to place narrow parameters on both programs. Agency materials state that parole in place is granted "only sparingly" and affirmatively endorses granting it only to the immediate relatives of members of the U.S. armed forces. When DHS does grant parole in place to an unlawfully present alien, however, the primary purpose is apparently to help the recipient to adjust status. Advance parole, according to agency materials, is available to unlawfully present aliens who receive many types of discretionary reprieves from removal (such as TPS and Deferred Enforced Departure), although DHS sometimes makes clear that it grants advance parole only for a narrow set of travel purposes, including to visit ill family members or attend their funeral. DHS does not appear to grant advance parole for the purpose of facilitating adjustment of status applications by unlawful entrants, but advance parole has that effect. An unlawfully present alien who receives a grant of advance parole and then leaves and reenters the United States pursuant to that grant is not subject to the three- or ten-year bar for unlawful presence. Those bars apply only to aliens who "depart" the United States after the period of unlawful presence, and under current case law, a trip abroad pursuant to a grant of advance parole does not count as a "departure" for purposes of those bars. The applicability of these forms of parole to unlawfully present aliens has generated controversy on both sides of the immigration debate. Some Members of Congress have criticized advance parole and its facilitation of adjustment of status applications as a loophole that subverts enforcement of the statutory bars for unlawful presence. The former INS, pursuing a similar theory, issued a regulation in 1997 that made many parolees ineligible for adjustment of status under INA Â§ 245(a), but multiple federal appellate courts struck down the regulation as incompatible with the statute and DHS repealed the regulation in 2006. On the other side of the debate, some immigration advocates have called for the expansion of parole in place and advance parole as a way to clear a path to legalization for a large segment of the unlawfully present population (namely, those eligible for immigrant visas on the basis of family relationships or other grounds). Even if the lawful entry requirement is met, INA Â§ 245(c)(2) generally bars aliens from adjusting status if they fail to maintain lawful status in any of three ways: (1) if they are "in unlawful immigration status on the date of filing the application for adjustment"; (2) if they have failed "to maintain continuously a lawful status since entry into the United States"; or (3) if they have engaged in "unauthorized employment." As such, Â§ 245(c)(2) generally bars unlawfully present aliens from adjusting status, even if they satisfy the lawful entry requirement, due to their lack of lawful immigration status. The Â§ 245(c)(2) bar does have exceptions, however. It does not apply to the immediate relatives of U.S. citizens. Thus, as already mentioned, if an alien overstays a nonimmigrant visa and then marries a U.S. citizen, the alien's failure to maintain lawful status does not bar an application for adjustment. Under other exceptions, the bar for failure to maintain lawful status also does not apply to certain domestic violence victims, certain "special immigrants," applicants for employment-based immigrant visas with a lapse or lapses in status not exceeding 180 days in the aggregate, and aliens who meet the April 30, 2001, cutoff date of INA Â§ 245(i). As the prior section explains, many unlawfully present aliens who are eligible to immigrate based on family relationships or other grounds do not qualify for adjustment of status because of the statutory requirements concerning lawful entry and maintenance of lawful status. These aliens, therefore, cannot obtain LPR status from within the United States. Such aliens may still pursue LPR status by departing the country and applying for an immigrant visa at a U.S. consulate abroad. Most unlawfully present aliens who take this route, however, encounter a significant obstacle: their departure from the United States triggers the three-year unlawful presence bar (for those who were unlawfully present for between 180 and 365 days) or the ten-year unlawful presence bar (for those who were unlawfully present for more than year). Aliens qualify for a discretionary waiver of these bars only if (1) they are the "spouse or son or daughter" of a U.S. citizen or LPRâthe parents of U.S. citizens or LPRs do not qualify; and (2) their inability to return to the United States during the applicable time bar (three or ten years from the date they departed the United States) would "result in extreme hardship" to their U.S. citizen (or LPR) parent or spouse. DHS interprets extreme hardship to mean "more than the usual level of hardshipÂ that commonly results from family separationÂ or relocation." Aliens who do not receive discretionary waivers must remain outside the United States for the duration of the bar, unless DHS grants them parole or they receive a discretionary waiver on a future visa application. Although the eligibility criteria for the unlawful presence waivers are narrow, DHS allows unlawfully present aliens to apply for the waivers from within the United States, before they depart for their visa interviews abroad, so long as the aliens are not inadmissible on other grounds and meet other requirements. This "provisional waiver" program mitigates the uncertainty that unlawfully present aliens face as to how long they will have to remain abroad if they leave the United States to apply for an immigrant visa. DHS introduced the provisional waiver program in 2013, but immigration authorities provided relief of a similar nature as early as 1935, when the Immigration and Naturalization Service (INS) began the practice of "pre-examining" unlawfully present aliens domestically before channeling them into immigrant visa application procedures in Canada. The following hypotheticals are intended to demonstrate how the INA provisions described in this section work in practice. Each hypothetical assumes that the alien (1) has not departed the United States after entry and (2) is not inadmissible to the United States for reasons other than unlawful entry or unlawful presence (such as a conviction for a crime of moral turpitude). 1. An alien is admitted to the United States on a B-2 tourist visa for six months. He overstays. Ten years later, he marries a U.S. citizen, who obtains an approved immigrant visa petition on his behalf. Even though the alien has been out of legal status for ten years, he is eligible to adjust to LPR status. He will not face the ten-year unlawful presence bar unless he departs the United States before obtaining LPR status. 2. Same facts as the previous example, except that the alien enters the United States surreptitiously rather than on a visitor visa. Even with an approved immigrant visa petition as the spouse of a U.S. citizen, he is not eligible to adjust status because of his unlawful entry. To obtain LPR status, he must apply for an immigrant visa at a U.S. consulate abroad. His departure from the country will trigger the ten-year unlawful presence bar. He may apply for a provisional waiver of the bar before departing, but he must show "extreme hardship" to his spouse to succeed on the application. 3. An alien enters the United States surreptitiously and subsequently has a daughter. After the daughter (a U.S. citizen) turns twenty-one, she obtains an approved immigrant visa petition for her mother. The mother is not eligible to adjust status due to her unlawful entry. To obtain LPR status, she must apply for an immigrant visa at a U.S. consulate abroad. Her departure from the country will trigger the ten-year unlawful presence bar, and she is not eligible for a waiver. 4. Same facts as the previous example, except that the U.S. citizen daughter is in the military. Her mother may qualify for parole in place, which would make her eligible to adjust status. In that scenario, the mother would not face the ten-year unlawful presence bar unless she departs the United States before obtaining LPR status. 5. An alien enters the United States surreptitiously at age eight. At age twenty-two, he receives a grant of Deferred Action for Childhood Arrivals (DACA). At age twenty-three, he marries a U.S. citizen, who obtains an approved immigrant visa petition on his behalf. The alien is not eligible to adjust status due to his unlawful entry. To obtain LPR status, he must apply for an immigrant visa at a U.S. consulate abroad. His departure from the country will trigger the ten-year unlawful presence bar. He may apply for a provisional waiver of the bar before departing, but he must show "extreme hardship" to his spouse to succeed on the application. 6. Same facts as the previous example, except that the alien, after receiving DACA and after the immigrant visa petition is approved, was granted advance parole to visit a sick family member abroad. Upon being paroled back into the United States following his trip abroad, he became eligible to adjust status. He will not face the ten-year unlawful presence bar unless he departs the United States before obtaining LPR status. The INA's cancellation of removal provision authorizes immigration judges to grant LPR status to some unlawfully present aliens who are in removal proceedings and who have lived in the United States for at least ten years. Aliens qualify, however, only if, aside from meeting other requirements, they show that their removal would cause "exceptional and extremely unusual hardship" to immediate relatives who are U.S. citizens or LPRs. The lineage of this form of relief extends back at least to 1935, when two members of President Franklin Roosevelt's cabinet, frustrated by the lack of a statutory mechanism to grant relief from deportation in hardship cases, used bureaucratic ingenuity to implement "a two-step procedure whereby the secretary [of labor] granted [an] illegal alien a waiver from deportation and allowed him or her to depart to Canada and to reenter the United States as a legal permanent resident." In 1940, Congress rendered this arrangement unnecessary by enacting the first clearly delineated statutory form of relief from deportation in hardship cases, which was called "suspension of deportation" until 1996. The Illegal Immigration Reform and Immigrant Responsibility Act (IIRIRA) of 1996 replaced "suspension of deportation" with "cancellation of removal," a more restrictive form of relief due in part to its higher threshold for qualifying hardship and its omission of hardship to the alien (as opposed to the alien's U.S. family) as a basis for relief. Under the current version of the INA, one form of cancellation of removal exists for LPRs in removal proceedings, and one exists for non-LPRs, including unlawfully present aliens. To qualify for non-LPR cancellation of removal, aliens must have been physically present in the United States for the ten years preceding their application, and, critically, they must make the requisite showing of "exceptional and extremely unusual hardship" to their U.S. citizen or LPR immediate relatives. "Exceptional and unusual hardship" means a level of hardship to an immediate relative that is "'substantially' beyond the ordinary hardship that would be expected when a close family member leaves this country." The paradigmatic case involves "a U.S. citizen child with a serious medical condition who, if [cancellation of removal] is denied, would be either involuntarily separated from her parent or relocated to a country where adequate medical treatment is not available." Aliens also must show good moral character and not have certain types of criminal convictions. Like adjustment of status, cancellation of removal is a discretionary form of relief, meaning that immigration judges retain discretion to deny it even to aliens who meet the statutory criteria. The INA caps cancellations of removal for non-LPRs at 4,000 per year, although the cap does not apply to some groups. If the cap has been reached in a particular fiscal year but the immigration judge determines that a cancellation of removal application should be granted, the judge must reserve decision until a subsequent fiscal year when cap spaces are available. Finally, cancellation of removal is available only as a defense to removal, meaning that aliens can apply for cancellation only if they are in removal proceedings. They cannot apply for relief affirmatively (i.e., outside of removal proceedings). When an immigration judge grants cancellation of removal to an unlawfully present alien, the alien becomes an LPR. Some commentators have thus called cancellation of removal a mechanism for "case-by-case legalization." But the major parameters for this mechanismâthe annual cap, the fact that aliens cannot apply for it affirmatively but instead only in removal proceedings, and the required hardship showingâsharply limit its availability. The lack of an affirmative channel for requesting cancellation of removal, in particular, has prompted some aliens who believe they clearly qualify for cancellation to proactively prompt DHS to initiate removal proceedings against them. The aliens do this, through their counsel, by making a special request to DHS or by filing an affirmative application for asylum, which upon denial triggers an automatic referral to removal proceedings. This strategy has pitfalls, however: it affirmatively triggers proceedings that could end in removal, and, in any event, immigration judges have discretion to dismiss the proceedings without granting cancellation upon determining that the alien filed "a meritless asylum application with the USCIS for the sole purpose of seeking cancellation of removal in the Immigration Court." Other mechanisms in the INA provide for the legalization of unlawfully present aliens who suffer particular types of harms. Asylum offers the prospect of LPR status to unlawfully present aliens who would face a risk of persecution if returned to their countries of origin, while the related protections of withholding of removal and relief under the Convention against Torture (CAT) offer more limited relief from persecution or torture. A series of nonimmigrant visas, including the U visa, offer the prospect of relief to unlawfully present aliens who are the victims or witnesses of certain crimes. Unlawfully present aliens may qualify for asylum, a lawful immigration status with a pathway to LPR status and citizenship, if they have suffered persecution in their country of origin or have a well-founded fear of suffering such persecution upon returning to that country. The general eligibility criteria for asylum include a requirement that the persecution be on account of an enumerated statutory ground (race, religion, nationality, membership in a particular social group, or political opinion). Aliens who have persecuted others or committed "serious crimes" are not eligible. The law of asylum is a broad subject that in most respects is conceptually distinct from the issue of legalization. Asylum is a general remedy for aliens in or at the threshold of the United States who suffer persecution, not a form of relief designed specifically for the unlawfully present population. However, asylum can work as a legalization mechanism in some cases. Lawful entry and maintenance of lawful status are not prerequisites to asylum. Periods of unlawful presence do not affect an alien's eligibility. Put differently, aliens present within the United States may qualify for asylum regardless of surreptitious entry or unlawful presence. Thus, for those unlawfully present aliens who have suffered persecution and meet the other statutory requirements, asylum, much like cancellation of removal, offers a path to LPR status. Unlike cancellation of removal, however, unlawfully present aliens may apply for asylum affirmatively. As relevant here, a few aspects of asylum law bear directly on the nature and availability of this form of relief to unlawfully present aliens. First, eligibility to apply for asylum is time-restricted. Although aliens may apply for asylum either affirmatively (i.e., on their own accord, even if the government is not seeking to remove them) or defensively (i.e., as a defense in removal proceedings), generally they must apply within one year of arriving in the United States. Thus, asylum is not available to most unlawfully present aliens who have been in the United States for long periods of time. Second, asylum offers a secure form of relief to unlawfully present aliens. Asylees are not subject to removal unless their status is terminated for a specified statutory reason; their spouses and minor children may apply to join them in the United States in asylee status; asylees are authorized to work; and, as already mentioned, they have a direct pathway to LPR status and therefore to citizenship. Unlawfully present aliens who do not obtain asylum may qualify for a more limited form of relief under the INA's provision for "restriction on removal" (commonly called "withholding of removal"), which prohibits the removal of aliens to a country where their "life or freedom would be threatened" on account of "race, religion, nationality, membership in a particular social group, or political opinion." Somewhat similarly, statutory and regulatory provisions implementing the Convention Against Torture prohibit the removal of aliens to any country in which there is substantial reason to believe they could be tortured. Unlike asylum, these two forms of relief do not create an avenue to LPR status and do not confer many of the other advantages typically associated with lawful immigration status, such as the ability to seek admission to the United States following a trip abroad or the ability to sponsor family members for admission. As such, withholding of removal and CAT protection arguably do not constitute legalization mechanisms, although they do confer a defense to removal and work authorization on recipients. Withholding and CAT protection also have a stricter burden of proof than asylum. In a different vein, unlike asylum, which is a discretionary form of relief, these two forms of relief are mandatoryâimmigration judges must grant them to eligible aliens. Nor do withholding of removal or CAT relief have one-year application deadlines. The INA authorizes DHS to grant three special nonimmigrant statuses to unlawfully present aliens who are victims or witnesses of certain crimes and who provide assistance to law enforcement. First and most broadly, aliens who suffer "substantial physical or mental abuse" from certain crimes committed against them in the United States (including rape, domestic violence, and kidnapping, among other qualifying offenses) and who assist in the investigation or prosecution of those crimes may qualify for nonimmigrant U visa status. Second, victims of sex trafficking or slavery trafficking who comply with "reasonable requests for assistance" from law enforcement may qualify for nonimmigrant T visa status if removal would cause them "extreme hardship." Third, aliens willing to provide "critical reliable information" about criminal or terrorist organizations may qualify for nonimmigrant S visa status. The INA caps U visas at 10,000 per year, T visas at 5,000 per year, and S visas at 250 per year across two subcategories (these caps do not apply to immediate family members who qualify derivatively). Recipients of each of the three statuses may adjust to LPR status if they satisfy specific statutory requirements. Of these three nonimmigrant statuses, U visa status has the broadest eligibility criteria and, as such, is the most frequently sought by unlawfully present aliens and also the most frequent subject of litigation and commentary. DHS has reached the statutory cap of 10,000 U visas in every fiscal year since 2010 and, as of the first quarter of FY2019, had a backlog of 234,114 pending U visa applications. Unlawfully present aliens on the waiting list for a U visa typically receive a discretionary reprieve from removalâdeferred action or parole. However, it takes an average of four years for DHS to vet applicants for eligibility before placing them on the waiting list and granting them deferred action or parole. Although the legalization mechanisms in the INA are narrow, U.S. immigration law has used two other methods to confer legal immigration status or other protections from removal on segments of the unlawfully present population: (1) ad hoc legalization laws that, rather than reforming the INA's generally applicable legalization provisions going forward, offer one-time relief or offer relief only for discrete populations, and (2) discretionary reprieves from removal, such as deferred action, that confer weaker protection sometimes described as "quasi-legal status." In the second half of the twentieth century, Congress enacted a major one-time legalization program and also enacted other ad hoc legalization measures for narrowly defined populations. The Immigration Reform and Control Act (IRCA) of 1986 contained two primary legalization measures that offered the prospect of LPR status to much of the population of aliens without legal status in the United States at that time. These were one-time legalization measures: they benefited only those aliens without legal status who had been in the United States since 1982 or who had performed agricultural work in the United States for at least ninety days between May 1985 and May 1986. The law specified a limited application period for both programs. The major rationale appears to have been that one-time legalization relief would not undermineâand might even advanceâthe deterrence of future illegal immigration, which was another major goal of IRCA. In other words, Congress appears to have reasoned that a one-time legalization program for aliens already in the United States, unlike a legalization mechanism baked into the regular framework of the INA, would not encourage aliens to enter or remain in the country in violation of the INA in the future. Aside from IRCA, Congress also enacted other legalization laws in the second half of the twentieth century that targeted particular nationalities rather than aliens present at a particular juncture. For example, the Cuban Adjustment Act of 1966, the Nicaraguan Adjustment and Central American Relief Act, and the Chinese Student Protection Act of 1992 all created special mechanisms for some aliens without legal status of particular nationalities to acquire LPR status or to seek LPR status under less exacting criteria than those generally applicable under the INA. A more recent law created a special permanent resident status for long-time residents of the Commonwealth of the Northern Mariana Islands facing revocation of immigration parole. Somewhat like IRCA, these laws created targeted relief for aliens who fell within specific parameters but did not alter the INA's generally restrictive approach to legalization for all other aliens. Proposed legalization legislation in the 21st century has generally followed the ad hoc mold of offering relief only to aliens who were unlawfully present in the United States during a specified time period or who fit within narrowly defined groups, or both. The various Dream Act proposals to create a pathway to LPR status for aliens without legal status who were brought to the United States as children, for example, would cover aliens who entered the United States before a particular date (usually several years before enactment) and who have resided in the United States since entry. Legalization provisions in comprehensive immigration reform bills that the Senate passed in 2006 and 2013, beyond providing for relief to childhood arrivals, also would have provided for relief to many or most unlawfully present aliens who lived in the United States during a specified time period and to certain agricultural workers. Other bills would create special adjustment of status mechanisms for recipients of TPS and Deferred Enforced Departure. All of these ad hoc proposals stand in contrast to less common proposals to amend the generally applicable legalization mechanisms in the INA going forward, such as proposals to advance the cutoff date for registry under INA Â§ 249 or for the adjustment of status mechanism for unlawfully present aliens in INA Â§ 245(i). In recent decades immigration authorities have increasingly exercised their enforcement discretion to grant unlawfully present aliens temporary reprieves from removal, such as deferred action, DACA, or TPS. These and other types of discretionary reprieves from removal, which are covered at more length in another CRS report, have thus become a significant aspect of the federal government's regulation of the unlawfully present population. Two events, in particular, did much to increase the number of aliens receiving discretionary reprieves: (1) the enactment of the TPS statute in 1990, which created a discretionary reprieve program for nationals of countries that the Secretary of DHS designates as unsafe for return because of armed conflict, natural disaster, or other extraordinary conditions, and (2) the executive branch's implementation of the DACA program in 2012 for certain unlawfully present aliens brought to the United States as children. Together, TPS and DACA appear to cover more than one million aliens whose presence in the United States violates the INA, although that figure may well decline in the near term as a result of recent executive branch efforts to terminate or curtail these reprieve programs. The grant of a discretionary reprieve constitutes an assurance from DHS that the recipient does not face imminent removal. Discretionary reprieves are not legalization mechanisms because they do not extinguish the basis of the alien's removability under the INA. They therefore do not offer steadfast protection from removal. For example, if an alien overstays a nonimmigrant visa and then receives a grant of deferred action from DHS, the risk remains that DHS will decide to pursue the alien's removal in the future. Yet discretionary reprieves typically confer other advantages, including eligibility for work authorization and the nonaccrual of unlawful presence during the duration of the reprieve. Legal scholars use an array of terms for the peculiar sort of relief that discretionary reprieves provide: "quasi-legal status," "liminal" or "twilight" status, and the "status of nonstatus." The INA subjects the more than ten million unlawfully present aliens in the United States to removal without a limitations period and gives them few opportunities to legalize. Political views of this generally restrictive approach to legalization differ: some favor creating expanded, mostly ad hoc pathways to legalization; others find the extant pathways to legalization too permissive and seek to curtail them. The debate is informed by the INA's current approach to legalization. The INA does not provide an avenue for an appreciable number of unlawfully present aliens to obtain lawful status based on long-standing presence, as the registry statute once did. The INA's penalties for unlawful entry and unlawful presence make it difficult for unlawfully present aliens to obtain lawful status based on qualifying family relationships (except, most notably, for nonimmigrant overstays who become immediate relatives of U.S. citizens). And it allows legalization on hardship grounds only in cases of truly extreme hardship to immediate relatives who are U.S. citizens or LPRs. Forms of humanitarian relief from persecution and other harms, such as asylum and the U visa program, do not exclude unlawfully present aliens from their reach but nonetheless have specific objectives and tailored eligibility criteria. Meanwhile, discretionary reprieves from removal and the quasi-legal status they confer upon unlawfully present aliens have become major components of the U.S. immigration system.

Summary: The population of unlawfully present aliens in the United States numbers between ten million and twelve million, according to recent estimates. The Immigration and Nationality Act (INA) takes three primary approaches to regulating this population: removal, deterrence, andâto a lesser extentâlegalization. Legalization, as used here, means the granting of a lawful immigration status to an unlawfully present alien so that he or she is no longer subject to removal under the INA. Put differently, an unlawfully present alien "legalizes" by obtaining lawful permanent resident status (LPR or "green card" status) or any other status (such as a nonimmigrant status) that extinguishes the statutory basis for his or her removal. The INA takes a generally restrictive approach to legalization. During much of the 20th century, a statutory provision called "registry" allowed unlawfully present aliens to obtain LPR status based on their long-standing presence in the United States. If unlawfully present aliens had entered the United States before a fixed cutoff date and satisfied other requirements, such as a lack of certain types of criminal convictions, they could apply to the Attorney General for LPR status. The registry statute is now effectively obsolete because its cutoff date, which Congress last updated in 1986, remains fixed at 1972. The most consequential body of legalization principles in the INA governs when unlawfully present aliens may obtain LPR status through qualifying family relationships or on other qualifying grounds. In general, the INA imposes barriers to the acquisition of LPR status for unlawfully present aliens who come within one of the three major categories that the law uses to select aliens for immigration to the United States: family-based immigrants, employment-based immigrants, and diversity immigrants. Specifically, most unlawfully present aliens who come within these categories must pursue LPR status by departing the United States to apply for an immigrant visa abroad (rather than applying to adjust status within the United States), and their departure typically triggers a ten-year bar on readmission to the United States. There are important exceptions to this general framework, however. In particular, an alien who overstays a nonimmigrant visa and then becomes the immediate relative of a U.S. citizen (through marriage, for example) may generally apply to adjust to LPR status without leaving the country and without facing any time bars on admission. Other INA provisions allow for legalization on hardship or humanitarian grounds. Cancellation of removal allows for legalization where the removal of an unlawfully present alien would cause hardship to immediate relatives who are U.S. citizens or LPRs, but the hardship must be "exceptional and extremely unusual." Cancellation of removal also is generally only available as a defense in removal proceedings (aliens cannot apply for it affirmatively), is subject to an annual cap, and, among other requirements, is only available to unlawfully present aliens who have been in the United States for at least ten years. As for humanitarian relief, asylum creates a pathway to LPR status for unlawfully present aliens who have a well-founded fear of persecution or suffered past persecution in their countries of origin. However, aliens generally must apply for asylum within one year of arriving in the United States (unless an exception applies), so asylum is not available to most unlawfully present aliens who have been in the country for long periods of time. Subsidiary protections from persecution and tortureâwithho lding of removal and protection under the Convention Against Torture (CAT)âdo not have the one-year application deadline, but they offer more limited relief that arguably does not qualify as lawful immigration status. Separately, a series of nonimmigrant statuses, including the U visa, offer the prospect of lawful immigration status to unlawfully present aliens who are victims or witnesses of certain crimes. U.S. immigration law has also taken other approaches to legalization, separate and apart from the narrow legalization provisions in the INA. First, Congress occasionally has enacted ad hoc legalization laws that, rather than reforming the INA's generally applicable provisions going forward, have offered one-time relief or relief only for discrete populations. Second, executive branch agencies have exercised enforcement discretion to grant unlawfully present aliens discretionary reprieves from removal, such as deferred action or the Deferred Action for Childhood Arrivals (DACA) initiative, which have conferred a weaker form of protection than lawful immigration status. This weaker form of protection is sometimes known as "quasi-legal status" and, although it typically confers work authorization and gives an unlawfully present alien an assurance that immigration authorities will not pursue his or her removal during a certain time, it does not extinguish the statutory basis for the alien's removal.