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 California, mass torts are civil actions that involve a large number of plaintiffs against one or a few defendants. These plaintiffs usually have similar legal issues or have been harmed in a similar manner by the defendant's actions. Mass torts often arise from exposure to harmful substances, defective products, or invasions of privacy, such as data breaches. While mass torts can be filed as class action lawsuits, they differ in that each plaintiff may have unique damages and the cases are often more complex. California courts handle mass torts through a coordinated process to manage the large volume of cases efficiently and to address common issues in a unified manner. This coordination can occur at the state level, known as Judicial Council Coordination Proceedings (JCCP), or at the federal level through Multidistrict Litigation (MDL). State statutes, case law, and procedural rules govern the conduct of mass tort litigation in California, ensuring that the rights of both plaintiffs and defendants are protected throughout the legal process.