A market is a system in which actors' transactions are limited by their resources and by legal rules that enforce transactions and prevent them from having severe effects on third parties. If transactions costs are not too high, the system yields efficient results by producing a state where further moves cannot improve anyone's lot without making someone else worse off. By contrast, in a regulatory system, people may trade only on terms or at times set by third parties. Trading under regulation produces an efficient result only if the regulator has set the same price that parties would have reached in their own bargaining. Criminal procedure is a method of allocating scarce resources. Police, judges, prosecutor, jails and jailers, and defense counsel are costly, and society gains by conserving their use. Crimes are even more costly. Efforts should aim at apportioning more resources to the criminal justice system until the savings from preventing the marginal crime just equal the costs of doing so. Further, the maximum deterrent effect should be achieved from whatever resources are committed to crime control. The latter objective tends to be achieved through the interactions of judges, prosecutors, and defendants in a market price-setting system. The appendix presents a model of plea bargaining that follows the settlement models of Gould and Landes. A total of 86 footnotes are provided.