Supplemental Jurisdiction
A federal court’s ability to hear related state-law claims that form part of the same case or controversy as a federal claim.
Governing rule: 28 U.S.C. § 1367
Plain-English definition
Supplemental jurisdiction lets a federal court keep closely related state-law claims alongside claims it already has power to hear. The idea is practical: if the claims come from the same nucleus of facts, one court can often resolve the whole dispute instead of splitting it between courts.
How it works
Courts may decline supplemental jurisdiction when the federal claims disappear early, the state issues dominate, or unusual circumstances make a state forum more appropriate.
Why it matters
Supplemental jurisdiction often determines whether a plaintiff can keep all claims together after a federal claim is dismissed.