The Supreme Court decided recently in Graham v. Florida that the Eighth Amendment prohibits a sentence of life in prison without parole for a nonhomicide crime committed by a minor. In its decision, the Court stated that “[t]he concept of proportionality is central to the Eighth Amendment” and that it is the “precept of justice that punishment for crime should be graduated and proportioned to [the] of- fense.” What about proportionality makes it a matter of justice? And how does proportionality cohere with our constitutional values? This Article addresses these questions.