A natural setting in which 158 coal miners who had filed grievances were assigned to either mediation or arbitration was used to test a model of 3 mediating processes underlying judgments of procedural justice: instrumental, noninstrumental, and procedural enactment. The generality of these processes was tested across procedures varying objectively in the degree of disputants' outcome control, across contexts in which disputes rather than decisions were resolved, and across situations in which the grievance was won, lost, or compromised as a result of the dispute resolution procedure. All 3 processes consistently accounted for judgments of procedural justice in all but 1 of these circumstances (instrumental processes did not account for procedural justice when grievants won). Perceptions of the 3rd party's enactment of the procedure emerged in this study as a key influence (as a moderator and mediator) of procedural justice judgments. Implications for the theory of procedural justice and the design of dispute resolution procedures are discussed.