This article considers the social desirability of prison work programs in a model in which the function of imprisonment is to deter crime. Two types of prison work programs are studied—voluntary ones and mandatory ones. A voluntary work program is socially beneficial: if prisoners are paid a wage that just compensates them for their disutility from work, the deterrent effect of the prison sentence is unaffected, but society obtains the product of the work program. But a mandatory work program is superior to a voluntary work program: if prisoners are forced to work without compensation, the deterrent effect of the prison sentence rises, allowing society to restore deterrence and save resources by reducing the probability of detection or the sentence length, and also to obtain greater output than under the optimal voluntary work program. In an extension of the basic analysis, however, in which prisoners vary in their disutility from work, a voluntary work program may be superior to a mandatory work program because prisoners with relatively high disutility from work can elect not to work.