Res judicata is hard enough already. Consider it at the interjurisdictional level, and we are asking for headaches. But consider it at that level we must, because litigation trends make interjurisdictional preclusion1 more important than ever. Lawyers, judges, litigants, and other litigation participants increasingly must contemplate the possibility that a lawsuit will have claim-preclusive or issue-preclusive effect in a subsequent suit in another jurisdiction. This article examines the problem of interjurisdictional preclusion, and, in particular, the problem of choice of preclusion law. Choice of-preclusion law cannot be appreciated in the abstract, but rather must be considered in light of litigation realities. Thus, the article conside...