Federal courts have federal-question jurisdiction in civil lawsuits that arise under the U.S. Constitution, federal laws, or treaties with other countries. Generally, this means that the lawsuit involves a cause of action created under federal law, like a violation of federal anti-discrimination laws. A lawsuit based on a violation of constitutional rights would also invoke a federal courts federal-question jurisdiction. In deciding such cases, the federal court would apply relevant federal law.
2. Diversity Jurisdiction Under 28 U.S.C. § 1332
If a federal court doesnt have federal-question jurisdiction, then it might still have diversity jurisdiction. Federal courts have diversity jurisdiction in civil cases where the amount in controversy is greater than $75,000 if there is whats known as complete diversity of citizenship between the plaintiffs and defendants in the case.