For many years, the unauthorized alien population has been seen as a public policy challenge. Addressing this population, estimated to number more than 11 million today, may take on added urgency in 2013 if the 113 th Congress tackles comprehensive immigration reform. Despite longstanding concern about the unauthorized population, however, there has not been much discussion about its composition. While the individuals included in this population at any point in time are officially categorized as unauthorized, they may differ significantly in their particular status-related circumstances under immigration law. For example, some unauthorized aliens in the United States have U.S. citizen or LPR family members or employers who are petitioning for them to become legal permanent residents (LPRs) of the United States under current law; others have no such sponsors. The variety of status-related circumstances among unauthorized aliens warrants attention because some immigration reform policy options under discussion would make distinctions based on individual circumstances. While there continue to be proposals seeking to establish statutory legalization programs to enable large numbers of unauthorized aliens to become LPRs or, conversely, proposals aimed at promoting the departure of large numbers of unauthorized aliens from the country over time, there also has been discussion of developing policies to provide targeted immigration relief to the unauthorized alien population. Immigration relief is a broad term that encompasses relief from removal from the United States without the granting of a legal immigration status as well as relief in the form of a legal immigration status, which could be a temporary immigration status or a permanent immigration status. A main focus of these various discussions about targeted relief has been limiting eligibility for legal status to certain segments of the unauthorized population. To help inform policy discussions about addressing the unauthorized alien population in these targeted ways, this report will analyze components of the unauthorized population and discuss policy options to provide relief to selected subgroups of particular congressional and public interest. According to recent estimates by the Department of Homeland Security (DHS), the unauthorized resident alien population totaled 11.5 million in January 2011. Using different sources, the Pew Hispanic Center estimated the unauthorized resident population at 11.1 million for March 2011. Both sets of estimates include individuals who are sometimes described as being "quasi-legal" because they have temporary authorization to remain in the United States but do not have a legal immigration status. These individuals include applicants for asylum (see Asylum under Other Avenues to Legal Immigration Status ) and persons with Temporary Protected Status (TPS) (see Other Forms of Immigration Relief ). DHS and Pew have analyzed the demographic characteristics of the unauthorized alien population. These characteristics help determine an individual's status-related prospects. Among the DHS and Pew findings, DHS estimated that about 85% of the unauthorized population in January 2011 had entered the country before 2005. With respect to labor force participation, Pew estimated that there were 8.0 million unauthorized aliens in the labor force in 2010, representing almost four of every five unauthorized adults in the United States that year. Pew also considered the U.S. families of unauthorized aliens, estimating that about half of all unauthorized adults (about 5 million individuals) were in families with minor children in 2010. About 1 million of these children were unauthorized aliens; another estimated 4.5 million children in families with at least one unauthorized parent were U.S.-born citizens. According to the Pew analysis, at least 9 million adults and children were in mixed-status families (i.e., families with at least one unauthorized parent and at least one U.S.-born child) in 2010. Under the Immigration and Nationality Act (INA), the basis of current immigration law, unauthorized aliens are typically unable to be legally employed and are subject to being removed from the country. They also have limited opportunities to obtain legal status while remaining in the United States. The INA prescribes pathways through which a foreign national can obtain legal temporary status and legal permanent status while in the United States. Nonimmigrants comprise the main category of legal temporary admissions. They include tourists, foreign students, and temporary workers, among others. Immigrants , synonymous with legal permanent residents , comprise the main category of legal permanent admissions. They consist primarily of family-based admissions (foreign nationals admitted on the basis of family ties) and employment-based admissions (foreign nationals admitted on the basis of employment ties or abilities). Also included among permanent admissions are humanitarian cases, such as individuals granted asylum on the basis of persecution claims. Foreign nationals in the United States—whether legally present or illegally present—who want to become LPRs and who are not eligible for humanitarian relief may lack the requisite family or employment relationships to obtain LPR status under the permanent family-based or employment-based immigration systems. In addition, the INA includes mechanisms, such as the grounds of inadmissibility, that may bar an unauthorized alien with the requisite ties from obtaining legal immigration status. In order to be eligible for a nonimmigrant or immigrant visa and for admission to the United States, a foreign national must be found to be admissible to the country. The INA enumerates grounds of inadmissibility—grounds upon which aliens are ineligible for visas and admission. They include health-related grounds and security- and terrorism-related grounds as well as grounds concerning illegal entrants, public charge (the likelihood that an alien will require public support), and other issues. Some grounds of inadmissibility may be waived, as specified in the INA. Selected grounds of inadmissibility, including those related to illegal entrants and illegal presence in the United States, are discussed separately below (see " Admissibility "). The following are key provisions in current law relevant to gaining legal nonimmigrant or immigrant admission to the United States while in the country. The provisions are introduced generally here to provide the background information necessary to discuss their application to unauthorized aliens. As explored briefly here and more fully in subsequent sections of this report, current law provides potential pathways for some components of the unauthorized resident population to obtain legal status, but not for others. Those without existing pathways would require new legislative enactments to become eligible for legal immigration status. Nonimmigrants are foreign nationals who are admitted to the United States for a temporary period of time and a specific purpose. Typically, they are admitted from abroad. The INA provides for lawfully admitted nonimmigrants to change from one nonimmigrant classification to another in the United States, with some exceptions and subject to certain conditions. It does not generally allow for unauthorized aliens to obtain legal nonimmigrant status. Unauthorized aliens, however, are able to obtain legal nonimmigrant status in limited cases. Under the INA, the Secretary of Homeland Security has broad discretionary authority to waive grounds of inadmissibility, including those related to illegal entry and unlawful presence, in the case of certain nonimmigrant categories. These categories include the "T" category for alien victims of severe forms of trafficking in persons and the "U" category for aliens who have suffered substantial physical or mental abuse as a result of being a victim of certain criminal activities. The INA also provides for eligible T nonimmigrants and U nonimmigrants to obtain LPR status under special provisions. More limited statutory exceptions to the INA inadmissibility provisions apply in the case of the "V" category for certain LPR spouses and children with pending immigrant visa petitions or pending applications for an immigrant visa or for adjustment of status. Adjustment of status , which is the subject of a succeeding section, is the process of becoming an LPR in the United States without having to go abroad to apply for a visa. Individuals in the United States applying for a V visa are not subject to the grounds of inadmissibility for illegal entrants, documentation, or unlawful presence (see " Admissibility ," below). Unlike T nonimmigrants and U nonimmigrants, however, V nonimmigrants need to adjust status under existing law. The INA provides for specified family members of U.S. citizens or LPRs and specified categories of workers to be admitted to the United States for permanent residence as LPRs. Both family-based immigration and employment-based immigration are subject to a complex set of preference categories and numerical limits. The process of becoming an LPR through either route has multiple steps. In most cases the sponsoring family member or employer must file an immigrant visa petition on behalf of the alien with DHS's United States Citizenship and Immigration Services (USCIS). There is no statutory restriction on submitting a visa petition on behalf of an illegally present alien. If the family-based or employment-based petition is approved, the State Department then must determine if a visa number is immediately available to the alien. Because of the numerical limits and their allocation among the various preference categories and countries of origin, it can take many years between the time an immigrant petition is filed and a visa number becomes immediately available to an alien. When a visa number becomes immediately available, the alien beneficiary can apply for assignment of a visa number. Aliens applying for visas abroad are subject to admissibility checks as part of that application process. Individuals who are issued visas become LPRs upon admission to the United States. Aliens eligible to adjust status, that is, obtain LPR status within the United States, do not have to go through the visa application process. They, however, are subject to admissibility checks as part of the adjustment of status process. Under current law, there are only limited opportunities for unauthorized aliens in the United States (with the requisite family or employment ties) to adjust to LPR status in the United States (see " Adjustment of Status ," below). Leaving the country to apply for a visa abroad, however, may pose risks (see " Admissibility ," below). Family-based immigrants are defined in the INA, by category. Top priority is given to immediate relatives of U.S. citizens. Immediate relatives include children, spouses, and, if the citizen is at least age 21, parents.