In this article I examine the social desirability of rewarding prisoners for good behavior, either by reducing their sentences (granting “time off”), converting part of their sentences to a period of parole, or providing them with privileges in prison. Rewarding good behavior reduces the state’s cost of operating prisons. But rewarding good behavior also tends to lower the deterrence of crime because such rewards diminish the disutility of imprisonment. I demonstrate that, despite this countervailing consideration, it is always socially desirable to reward good behavior with either time off or parole. In essence, this is because the reward can be chosen so that it just offsets the burden borne by prisoners to meet the standard of good behavior — resulting in good behavior essentially without a reduction in deterrence. While employing privileges to reward good behavior might be preferable to no reward, the use of privileges is inferior to time off and parole.