Redundancy is a four-letter word. According to courts and scholars, redundant litigation is costly, unfair, and confounding. Modern civil procedure has a ( nearly) maximalist preference for centralization, and various rules seek to limit duplicative suits within and across court systems. This seemingly dominant view stands in marked contrast to the reality of the modern regulatory state. Redundant public-private enforcement, in which public and private actors have overlapping authority to enforce the law, is ubiquitous. Redundant enforcement also is noticeably underrepresented in the substantial literature on private and public enforcement, which typically treats government agencies and private attorneys general as substitutes rather than complements. This Article seeks to fill these gaps. It begins with a survey of the myriad forms of redundant enforcement in U.S. law, and then turns to a defense of redundant public-private enforcement. Scholars of engineering and public administration have built up a powerful literature on the potential uses of redundancy, and this Article applies those insights to overlapping public and private enforcement in U.S. law. Drawing on those literatures, this Article derives principles of redundant enforcement that account for the diversity of agents and the potential for strategic behavior. It argues that redundancy may be an effective response to errors, resource constraints, information problems, and agency costs, if redundant-enforcement regimes harness multiple diverse agents and are tailored to the relevant regulatory environment. Specifically, if the lawmaker worries that public or private agents are missing good cases, redundant authority may help to reduce errors, increase resources, aggregate information, and improve monitoring-though permitting duplicative suits may undercut these gains. Meanwhile, if the lawmaker is concerned about under-enforcing settlements or judgments, symmetrically non-preclusive redundant litigation may be a valuable tool-though damages should offset to avoid multiple punishments, and procedural rules should maintain incentives and allocate cases.
