Multidistrict litigation, or MDL, is the mechanism federal courts use when large numbers of separately filed cases across the country share common factual questions, a defective drug, a data breach, a faulty product. The Judicial Panel on Multidistrict Litigation, a specialized panel of federal judges, can transfer those cases into a single district for coordinated pretrial proceedings: shared discovery, consolidated motion practice, unified expert and Daubert rulings, and case management overseen by one judge instead of dozens. This avoids the waste of hundreds of courts independently re-litigating the same core factual questions about how a product failed or a company behaved, and it is the dominant procedural vehicle for modern mass tort and product liability litigation.

The defining limit on MDL is that Section 1407 consolidation is for pretrial purposes only. It does not merge the transferred cases into one action, and each plaintiff generally retains an individual case and individual counsel rather than joining a single class-wide claim. Absent a global resolution, cases are eventually remanded back to their originating districts for individual trial. In practice, most MDLs never reach that point because the transferee court schedules bellwether trials, a handful of representative cases tried to verdict or otherwise resolved, to generate real information about how similar cases are likely to be valued and resolved.

MDL is often confused with a class action, but the two work differently. A class action creates one unified proceeding with a class-wide binding judgment or settlement covering everyone in the class by default. An MDL is a coordination device: plaintiffs keep separate cases and separate claims, coordinated only for efficiency, typically organized through a leadership structure of lead counsel and a plaintiffs' steering committee representing the group in dealings with the transferee court and the defense. That leadership structure, not a class definition, is what holds a sprawling MDL together procedurally.

Mass tort and product liability litigants rely on MDL to avoid duplicating discovery across hundreds or thousands of nearly identical cases, concentrating the fight over causation, defect theory, and damages methodology before one judge. Bellwether trial results and leadership-negotiated settlement matrices then ripple through the entire consolidated docket, so which handful of cases gets selected as bellwethers, and how they turn out, can effectively set the value of thousands of unrelated individual claims still waiting behind them.