Federal immigration law governs both the exclusion of aliens from admission to this country and the deportation of aliens previously admitted. Two kinds of actions occurred in different procedural settings for both deportation and exclusion. Now, as before, the immigration laws provide two separate lists of substantive grounds, principally involving criminal offenses, for these two actions. One list specifies what kinds of crime render an alien excludable (or in the term the statute now uses, “inadmissible”), see § 1182(a) (2006 ed., Supp. IV), while another--sometimes overlapping and sometimes divergent--list specifies what kinds of crime render an alien deportable from the country, see § 1227(a). Section 212(c) of the Immigration and Nationality Act authorized the Attorney General to admit certain excludable aliens. D could order this relief when the alien had lawfully resided in the United States for at least seven years before temporarily leaving the country unless the alien was excludable on one of two specified grounds. Discretionary relief was available for exclusion for not for deportation. Deportable aliens who had traveled abroad and returned could receive §212(c) relief, while those who had never left could not. Congress substituted a new discretionary remedy, known as “cancellation of removal,” which is available in a narrow range of circumstances to excludable and deportable aliens alike. Deciding whether to exclude an alien is an easy matter. Deciding whether to deport an alien, applying § 212(c) becomes a tricky business. Section 212(c) applies on its face only to exclusion decisions. So, the question arises: How is the BIA to determine when an alien should receive § 212(c) relief in the deportation context? The “comparable-grounds” rule is used. If the deportation ground consists of a set of crimes “substantially equivalent” to the set of offenses making up an exclusion ground, then the alien can seek §212(c) relief. P, who has lived continuously in the United States as a lawful permanent resident since 1974, pleaded guilty to voluntary manslaughter in 1988. After he pleaded guilty to another crime in 2005, Holder (D) commenced a deportation action, charging him with having committed an “aggravated felony” involving “a crime of violence” based on his manslaughter conviction. P, who has lived continuously in the United States as a lawful permanent resident since 1974, pleaded guilty to voluntary manslaughter in 1988. After he pleaded guilty to another crime in 2005, Holder (D) commenced a deportation action, charging him with having committed an “aggravated felony” involving “a crime of violence” based on his manslaughter conviction. The Immigration Judge ordered D's deportation, and the BIA affirmed, finding P ineligible for § 212(c) relief because the “crime of violence” deportation ground is not comparable to any exclusion ground. The Ninth Circuit denied P’s petition for review. The Supreme Court granted certiorari.