The proliferation of mass litigation, in which many plaintiffs sue a common defendant or defendants, for injuries from the same accident, or from exposure to the same product or substance, reflects the increasingly collective nature of life in the second half of the twentieth century. This article, reprinted from Law and Contemporary Problems, examines the impact of aggregative procedures on mass tort litigation. It draws on a series of case studies of seventeen mass tort litigations that vary across important dimensions such as: (1) the type of formal and informal aggregative procedure used, (2) the type of product, exposure or incident that generated the litigation, (3) the types of injuries that resulted, and (4) the geographical scope of the litigation and of the aggregative procedure. The authors focus on the role of courts in mass tort litigation. They first describe courts' interests in such cases and then consider the power that courts have to aggregate claims, describing limits on that power and the flexibility that courts have to get around limits. Finally, they examine how courts' interests in resolving mass tort litigation interfere with judicial promulgation and consistent application of legal rules. The characteristics of mass litigation have often forced courts far from the ideal that they carefully and fairly consider the merits of each case, balance the interests of parties, and articulate and apply rules for society. The traditional legal process cannot determine the individual merits of tens or hundreds of thousands of claims against scores of defendants. Courts have no special expertise in balancing the interests of present and future claimants, a tradeoff that is present in every mass tort involving latent injuries. Finally, when faced with mass torts, courts are not simply disinterested administrators of justice. Rather, the extraordinary burdens of mass litigation make them deeply interested participants. Even though judicial concerns are both worthy and reasonable, we must still be concerned about how courts balance their own interests against the interests of others as they wield their enormous power to shape mass tort cases. The courts' interests might compromise the essential judicial duties to articulate sensible legal rules and to apply those rules in a consistent manner.