February 11, 2026
Mass Actions, Mass Torts, and the Rise of Multidistrict Litigation

When Americans think about civil litigation, we tend to imagine its bilateral form: Company A sues Company B, or John Roe sues Jane Doe. That model works when disputes are discrete, parties are evenly matched, and harms are easily traced. It breaks down, however, when injuries are widespread, claims are too small to justify individual pursuit, and thousands of plaintiffs confront a single, well-resourced defendant.
Those conditions gave rise to what we now call mass actions—procedural mechanisms that aggregate claims without extinguishing individual rights. This post traces the evolution of American mass actions from their equitable origins, through Rule 23 class actions, to the modern dominance of multidistrict litigation (“MDL”). Its purpose is to explain how, across each stage of its development, the system moved and evolved in order to tackle the same core problem: how to capture the efficiencies of collective adjudication while preserving individualized justice.
The Equitable Origins of Mass Actions
For roughly the first 150 years of American civil practice, what we would now recognize as class actions existed in equity, borrowing from English Chancery traditions. Former Equity Rule 48 permitted representative litigation where a common or general interest affected a class so numerous that joinder was impracticable. Courts used these bills in equity to cluster related claims, creating an early—if imperfect—form of aggregation.
These tools, however, were ill-suited to large-scale disputes. Among other things, they offered no uniform standard for representation, limited mechanisms for managing individualized issues, and little guidance for balancing efficiency against fairness, including whether absent parties would be bound. As collective harms grew larger and more complex, these limitations became more pronounced.
The Adoption of Rule 23 and the Birth of the Class Action
The adoption of Federal Rule of Civil Procedure 23 in 1938 marked a turning point. Rule 23 replaced ad hoc equitable practices with a codified framework defining when a small number of plaintiffs could litigate on behalf of many. Rule 23 introduced a new codified framework in 1938, later refined by the 1966 amendments into today’s familiar certification requirements—numerosity, commonality, typicality, adequacy, predominance, and superiority—meant to ensure that aggregation serves both efficiency and fairness.
Rule 23 works best where common questions truly drive the case. But as mass disputes expanded—particularly in products liability and antitrust—its limitations became apparent. Variations in exposure, injury, causation, damages, and governing law strain the class model. Under Rule 23(b)(3), courts certify a class only if common questions predominate—a demanding standard that frequently defeats certification in mass torts. Beyond doctrine, this mismatch raises fairness and due-process concerns, as aggregation risks resolving individualized questions of liability and damages through procedural shortcuts ill-suited to protect either side’s substantive rights.
The Creation of the JPML and the Rise of the MDL
Congress responded in 1968 by creating the Judicial Panel on Multidistrict Litigation. That structure authorizes transfer of civil actions with common factual questions to a single federal court for coordinated pretrial proceedings. Unlike class actions, MDLs preserve the separateness of each plaintiff’s case while centralizing work that benefits from scale, including motions to dismiss, summary judgment, and Daubert proceedings.
In practice, transferee judges appoint leadership counsel, coordinate discovery, resolve common dispositive and evidentiary motions, conduct bellwether trials, and facilitate global settlement discussions. The MDL’s central innovation is procedural coordination without substantive consolidation. Each plaintiff formally retains an individual claim, remedy, and trial right, while the system avoids duplicative rulings and inconsistent outcomes and preserves Article III adjudication of individual disputes.
Amchem, Ortiz, and the Limits of Settlement-Only Class Actions
Supreme Court decisions in Amchem Products, Inc. v. Windsor and Ortiz v. Fibreboard Corp. sharply limited the availability of settlement-only mass tort class actions. The Court held that Rule 23’s requirements apply with full force even when certification is sought solely to effect a global settlement, emphasizing rigorous scrutiny of adequacy, predominance, and intra-class conflicts in heterogeneous litigations. In other words, settlement convenience could not cure structural mismatches between the class device and the individualized nature of mass tort claims.
These decisions did not eliminate class actions. But they underscored why mass torts rarely fit comfortably within them—and why MDLs emerged as the system’s primary alternative. Their practical import was to effectively close the door to using Rule 23 as a vehicle for mandatory, one-shot global peace in tort, channeling resolution toward MDL-based private ordering—bellwethers, negotiated matrices, and opt-in inventory settlements—while preserving each plaintiff’s trial right. They also shifted innovation elsewhere: toward issue classes under Rule 23(c)(4), parens patriae actions by sovereigns, and, in some instances, bankruptcy or “Texas two-step” strategies to obtain non-class global resolutions—developments that further entrenched the MDL as the central forum for mass tort resolution.
Why MDL Endures
MDL’s durability reflects institutional alignment rather than doctrinal accident. For plaintiffs, MDLs offer scale—shared discovery, coordinated motion practice, and settlement leverage—without forfeiting individual claims or trial rights. For defendants, they provide predictability and efficiency by centralizing pretrial proceedings, reducing duplicative costs, and mitigating inconsistent rulings across jurisdictions. For courts, MDLs conserve scarce judicial resources while preserving adjudicatory limits by restricting consolidation to the pretrial phase. For the justice system, MDLs supply a flexible framework that absorbs heterogeneity without collapsing into either unmanageable fragmentation or overinclusive aggregation. That convergence explains why the MDL has become the default architecture for modern mass tort litigation—and why it has proven resilient despite critique.
The Design Challenge That Endures
Modern practice selects among procedural tools based on fit. Class actions remain essential where common issues predominate. MDLs dominate where common facts justify coordination but individualized harms demand separation. Together, these mechanisms keep the civil justice system workable—and meaningful—when harms scale beyond the individual case. The enduring challenge is deploying these tools with discipline, judiciously retaining the benefits of individual justice, while capitalizing on the benefits of aggregation.
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