A procedural device in federal civil procedure (Rule 23) that permits one or more individuals to represent and litigate claims on behalf of a larger group sharing common legal or factual issues, allowing adjudication in Article III courts. By aggregating many similar claims—subject to certification standards clarified in cases such as Wal‑Mart Stores, Inc. v. Dukes (2011)—it increases judicial efficiency, broadens access to remedies, and facilitates private enforcement of regulatory and consumer protections.