A mass tort is a civil lawsuit that involves hundreds or thousands of plaintiffs and one or a few defendants in which the plaintiffs have the same or similar claims against the defendant or defendants. Mass tort lawsuits are often filed as class action lawsuits (a procedural mechanism for joining the plaintiffs in one lawsuit), and are typically based on alleged wrongful acts (torts) such as exposure of the plaintiffs to harmful substances (asbestos or benzene), or defective products (pharmaceuticals or medical devices), or invasions of privacy (data breaches).

In Illinois, mass torts are civil actions that involve a large number of plaintiffs against one or a few defendants. These plaintiffs generally have similar legal grievances against the defendant(s), often arising from harmful exposures, defective products, or privacy violations. Illinois courts handle mass torts in a manner that may consolidate cases for pretrial proceedings to manage the litigation efficiently. This is done to avoid inconsistent rulings and to conserve resources. While mass torts can be filed as class actions, they are distinct in that each plaintiff may have unique damages and the cases are often more complex. Class actions require certification by the court, which will consider factors such as the numerosity of plaintiffs, commonality of legal or factual issues, typicality of claims or defenses, and adequacy of representation. If certified, the class action allows plaintiffs to pursue their claims collectively. It's important to note that both federal and state laws, including the Illinois Class Action Act, can govern the procedures and requirements for these types of lawsuits.