Life imprisonment sentences are rare in the federal criminal justice system. Virtually all offenders convicted of a federal crime are released from prison eventually and return to society or, in the case of illegal aliens, are deported to their country of origin. Yet in fiscal year 2013 federal judges imposed a sentence of life imprisonment without parole on 153 offenders. Another 168 offenders received a sentence of a specific term of years that was so long it had the practical effect of being a life sentence. Although together these offenders represent only 0.4 percent of all offenders sentenced that year, this type of sentence sets them apart from the rest of the offender population. This report examines life sentences in the federal system and the offenders on whom this punishment is imposed. There are numerous federal criminal statutes that authorize a life imprisonment sentence to be imposed as the maximum sentence. The most commonly used of these statutes involve drug trafficking, racketeering, and firearms crimes. Additionally, there are at least 45 statutes that require a life sentence to be imposed as the minimum penalty. These mandatory minimum penalties generally are required in cases involving the killing of a federal official or other government employee, piracy, or repeat offenses involving drug trafficking or weapons. In fiscal year 2013, 69 of the 153 offenders who received a sentence of life imprisonment were subject to a mandatory minimum penalty requiring the court to impose that sentence.