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 Iowa, as in other states, a mass tort is a type of civil action involving numerous plaintiffs against one or a few defendants where the claims are similar in nature. These cases often arise from exposure to harmful substances, defective products, or privacy violations such as data breaches. While mass torts can be filed individually, they are frequently brought as class action lawsuits, which allows for the consolidation of the plaintiffs' cases to improve efficiency and consistency in the legal process. Class actions in Iowa are governed by Iowa Rules of Civil Procedure, specifically Rule 1.261 to 1.263, which outline the requirements for certifying a class, including numerosity, commonality, typicality, and adequacy of representation. Federal mass torts may also be consolidated into multidistrict litigation (MDL) to streamline pretrial proceedings when cases are filed in different federal districts. It's important to note that mass torts differ from typical class actions in that each plaintiff may have unique damages and issues that require individual assessment, even though they share common factual or legal issues.