This chapter explores the conceptual connection between collateral estoppel and the preclusion doctrine of virtual representation. It points out the difference between estoppel, which can only benefit nonparties, and virtual representation, which allows nonparties to be adversely bound by judgments. This chapter also offers an account of the jurisprudential debate in American law about the appropriateness of virtual representation and the related Supreme Court precedents to show how this doctrine must not be taken pro tanto as adequate representation, a due process requirement in class actions, to justify preclusion simply by prior litigation of the same issue by someone with the same interest. Finally, it argues that nonparties can assert preclusion in their benefit but cannot be bound aversely by judgments given in cases without their participation or consent, which is the appropriate interpretation of collateral estoppel in light of class actions, virtual and adequate representation and the individual right to a day in court.