It has become commonplace to say that restorative justice cannot be defined. I argue that restorative justice can and must be defined concretely as a justice mechanism. I develop this argument with four points: (1) restorative justice is not a type of justice, it is a justice mechanism; (2) retributive justice is not a type of justice or a justice mechanism; (3) restorative justice is one of many justice mechanisms under an innovative justice umbrella; and (4) restorative justice can be defined. The way forward is to assess and compare a variety of justice mechanisms, which reside on a continuum from conventional to innovative. In time, the justice mechanisms studied may come to matter more than the concept of restorative justice.