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 Arizona, a mass tort is a type of legal action where many plaintiffs bring a lawsuit against one or a few defendants due to similar harm caused by the defendants' actions or products. These cases often involve issues like exposure to hazardous materials, defective products, or large-scale privacy breaches. While mass torts can be filed individually, they are frequently handled as class action lawsuits, which allows for the consolidation of numerous similar individual claims into a single action for efficiency and consistency. This procedural consolidation is governed by both state rules and federal laws, such as the Federal Rules of Civil Procedure for class actions that may apply if the case is in federal court. Arizona follows the Arizona Rules of Civil Procedure, which outline the requirements for certifying a class action, including numerosity, commonality, typicality, and adequacy of representation. Mass torts are complex and require careful coordination, often involving multidistrict litigation (MDL) when cases are federal to streamline pretrial proceedings when cases from multiple jurisdictions are involved.