What is the act of joining parties or claims in a single lawsuit known as?

The act of joining parties or claims in a single lawsuit is known as joinder. Joinder allows multiple parties or claims to be brought together in a single action, promoting judicial efficiency and preventing the fragmentation of related claims or disputes. This facilitates a comprehensive resolution of issues and reduces the likelihood of conflicting judgments or duplicative litigation.

While compulsory joinder specifically refers to situations where a party must be added to a lawsuit because their inclusion is necessary for complete relief or to avoid prejudice, and permissive joinder allows parties to join together in a lawsuit if their claims share common questions of law or fact, both fall under the broader concept of joinder. Supplemental jurisdiction, on the other hand, pertains to a court's authority to hear additional claims that are related to the original jurisdiction despite not meeting the original requirements for federal jurisdiction. Thus, the correct answer encapsulates the general term that encompasses all types of joining parties or claims in legal proceedings.