Congress has broad plenary authority to determine classes of aliens who may be admitted into the United States and the grounds for which they may be removed. Pursuant to the Immigration and Nationality Act (INA), as amended, certain conduct may either disqualify an alien from entering the United States or provide grounds for his or her removal. Prominently included among this conduct is criminal activity. In general, aliens may legally enter the United States under one of three categories: (1) legal permanent residents (LPRs), who are also commonly referred to as immigrants; (2) nonimmigrants, who are aliens permitted to enter the United States temporarily for a specific purpose, such as for tourism, academic study, or temporary work; and (3) refugees, who are aliens facing persecution abroad and are of special humanitarian concern to the United States. There are two aspects for legal admission under each of these categories. First, an alien must fulfill the substantive requirements for admission under a specified category. For example, in order to enter the United States as a nonimmigrant student, an alien must demonstrate that he is a bona fide student at an approved school. Second, aliens who fulfill substantive requirements for admission may nevertheless be denied admission if they fall within a class of inadmissable aliens listed under INA § 212. Once admitted, aliens remain subject to removal if they fall within a class of deportable aliens listed under INA § 237. The INA contains bars for admission and grounds for deportation based on criminal conduct. This report discusses the potential immigration consequences of criminal activity. "Criminal activity" generally refers to conduct for which an alien has been found or plead guilty before a court of law, though in limited circumstances consequences may attach to the commission of a crime or admission of acts constituting the essential elements of a crime. Consequences may flow from violations of either federal, state or, in many circumstances, foreign criminal law. Some federal crimes are set out in the INA itself—alien smuggling, for example. However, not all violations of immigration law are crimes. Notably, being in the United States without legal permission—i.e., being an "illegal alien"—is not a crime in and of itself. Thus, for example, an alien who overstays a student visa may be an "illegal alien," in that the alien may be subject to removal from the United States, but such an alien is not a "criminal alien." For several decades, the primary authority to interpret, implement, and enforce the provisions of the INA was vested with the Attorney General. The Attorney General delegated most authority over immigration matters to two bodies within the Department of Justice (DOJ): the Immigration and Naturalization Service (INS), which was delegated authority over immigration enforcement and service functions, and the Executive Office of Immigration Review (EOIR), which was delegated adjudicatory functions over immigration matters. Following the establishment of the Department of Homeland Security (DHS), the INS was abolished and its functions were transferred to DHS. Pursuant to INA § 103(a)(1), as amended, the DHS Secretary is now "charged with the administration and enforcement of ... [the INA] and all other laws relating to the immigration and naturalization of aliens, except insofar as this chapter or such laws relate to the powers, functions, and duties conferred upon the ... [other executive officers and agencies including] the Attorney General...." Pursuant to INA § 103, as amended, EOIR retains adjudicative authority over immigration matters, and rulings by the Attorney General with respect to questions of immigration law remain controlling upon immigration authorities. However, the precise scope of the Attorney General's continued authority over other immigration matters remains unclear, because most provisions of the INA have not been specifically amended to reflect the transfer of certain immigration functions to DHS. As a result, many of the regulations implemented by DHS and EOIR are presently duplicative or otherwise overlapping. The Homeland Security Act of 2002, which established DHS and transferred to it many immigration functions previously conducted by the INS, provided a general guideline that immigration officials to whom immigration functions were transferred "may, for purposes of performing the function, exercise all authorities under any other provisions of law that were available with respect to the performance of that function to the official responsible for the performance of the function immediately before [transfer]." As a practical matter, the DHS has primary day-to-day authority over immigration matters, while the Attorney General and EOIR maintain adjudicatory authority over immigration matters and questions of immigration law. The INA lists a number of criminal grounds for designating an alien as inadmissible or deportable. Most crimes included under these grounds are not specifically mentioned, but instead fall under a broad category of crimes, such as crimes involving moral turpitude or aggravated felonies . In addition, certain criminal conduct precludes a finding of good moral character under the INA, thereby preventing an alien from becoming either a naturalized U.S. citizen or a candidate for certain types of relief. The class of crimes involving moral turpitude , the class of aggravated felonies , and the class of crimes that preclude a finding of good moral character are overlapping, but no two classes are coextensive. The types of crimes constituting crimes of moral turpitude are determined by case law. Crimes that are aggravated felonies are listed in statute, with case law illuminating the bounds of certain listed crimes. Crimes precluding a finding of good moral character are determined by a combination of case law and statutory law. These criminal classes are further modified for the purposes of specific INA provisions. The following sections will describe these criminal categories in more detail. Immigration law has used the term "moral turpitude" in its criminal grounds for exclusion since 1891. Whether a crime involves moral turpitude has been determined by judicial and administrative case law rather than a statutory definition. In general, if a crime manifests an element of baseness or depravity under current mores—if it evidences an evil or predatory intent—it involves moral turpitude. Thus, certain crimes such as murder, rape, blackmail, and fraud have been considered crimes involving moral turpitude, whereas crimes such as simple assault have not been considered to involve moral turpitude. Since 1988, Congress has designated specific offenses as aggravated felonies for immigration purposes, and it has made removal of aliens convicted of such crimes a priority through streamlined procedures and ineligibility for various types of relief. Aggravated felonies were initially listed under the INA pursuant to the Anti-Drug Abuse Act of 1988 as part of a broad effort to combat narcotics trafficking. The only crimes designated in the 1988 Act were murder, drug trafficking, and illegal trafficking in firearms or destructive devices. Subsequent legislation has expanded the definition of "aggravated felony" a number of times, to include certain categories of crimes and many specific crimes. Section 101(a)(43) of the INA defines "aggravated felony" through the listing of a number of criminal categories and specified crimes. The broadest categories of aggravated felonies under the INA are as follows: any crime of violence (including crimes involving a substantial risk of the use of physical force) for which the term of imprisonment is at least one year; any crime of theft (including the receipt of stolen property) or burglary for which the term of imprisonment is at least one year; and illegal trafficking in drugs, firearms, or destructive devices. Many specific crimes are also listed as aggravated felonies under the INA. These include the following: murder; rape; sexual abuse of a minor; illicit trafficking in a controlled substance, including a federal drug trafficking offense; illicit trafficking in a firearm, explosive, or destructive device; federal money laundering or engaging in monetary transactions in property derived from specific unlawful activity, if the amount of the funds exceeded $10,000; any of various federal firearms or explosives offenses; any of various federal offenses relating to a demand for, or receipt of, ransom; any of various federal offenses relating to child pornography; a federal racketeering offense; a federal gambling offense (including the transmission of wagering information in commerce if the offense is a second or subsequent offense) which is punishable by imprisonment of at least a year; a federal offense relating to the prostitution business; a federal offense relating to peonage, slavery, involuntary servitude, or trafficking in persons; any of various offenses relating to espionage, protecting undercover agents, classified information, sabotage, or treason; fraud, deceit, or federal tax evasion, if the offense involves more than $10,000; alien smuggling, other than a first offense involving the alien's spouse, child, or parent; illegal entry or reentry of an alien previously deported on account of committing an aggravated felony; an offense relating to falsely making, forging, counterfeiting, mutilating, or altering a passport or immigration document if (1) the term of imprisonment is at least a year and (2) the offense is not a first offense relating to the alien's spouse, parent, or child; failure to appear for service of a sentence, if the underlying offense is punishable by imprisonment of at least five years; an offense relating to commercial bribery, counterfeiting, forgery, or trafficking in vehicles with altered identification numbers, for which the term of imprisonment is at least one year; an offense relating to obstruction of justice, perjury or subornation of perjury, or bribery of a witness, for which the term of imprisonment is at least one year; an offense relating to a failure to appear before a court pursuant to a court order to answer to or dispose of a charge of a felony for which a sentence of two years' imprisonment or more may be imposed; and an attempt or conspiracy to commit one of the foregoing offenses.