Preclusion law is notoriously convoluted. Courts have made no secret of their distaste for the doctrine, describing it variously as “conflicting,” “inconsistent,” “breeding confusion,” and ultimately “not very well liked.” Though the Supreme Court has consolidated issue and claim preclusion into a single coherent whole, this Note argues that the merger of res judicata and collateral estoppel in our modern preclusion law is incomplete. These different preclusions are motivated by different rationales: Res judicata protects private closure of parties, while estoppel began as a defense of judicial interests and expanded to forward systemic ones. Though private and systemic interests may often align, this alignment is not inevitable. In the case of public rights, failure to keep these doctrines distinct has undermined judicial ability to offer closure. Attention to the differences in historic preclusion doctrines ultimately provides a direction for modernization in the form of intervention.