"Federal courts," we have often explained, "are courts of limited jurisdiction." E.g., Kokkonen v. Guardian Life Ins. Co. of America, 511 U. S. 375, 377 (1994). Limited first by the Constitution, to only the kinds of "Cases" and "Contro-versies" listed in Article III. And for all lower federal courts, limited as well by statute. Congress determines, through its grants of jurisdiction, which suits those courts can resolve. So, for example, Congress has always given federal courts power to decide "diversity" cases, between "citizens of different States" whose dispute involves more than a stated sum (the so-called amount-in-controversy). §1332(a). And of special importance here, Congress has long conferred jurisdiction on federal courts to resolve cases "arising under" federal law. §1331.
"Arising under" jurisdiction—more often known as fed-eral-question jurisdiction—enables federal courts to decide cases founded on federal law. A suit most typically falls within that statutory grant "when federal law creates the cause of action asserted." Gunn v. Minton, 568 U. S. 251, 257 (2013). On rare occasions, the grant also covers a suit containing state-law claims alone, because one or more of them "necessarily raise[s]" a "substantial" and "actually disputed" federal question. Id., at 258. Either way, the determination of jurisdiction is based only on the allegations in the plaintiff's "well-pleaded complaint"—not on any is-sue the defendant may raise. Franchise Tax Bd. of Cal. v. Construction Laborers Vacation Trust for Southern Cal., 463 U. S. 1, 9–10 (1983). That longstanding rule makes the complaint—the plaintiff's own claims and allegations—the key to "arising under" jurisdiction. If the complaint presents no federal question, a federal court may not hear the suit.
But if a complaint includes the requisite federal question, a federal court often has power to decide state-law ques-tions too. Suppose a complaint with two claims—one based on federal, the other on state, law. This Court held in Mine Workers v. Gibbs, 383 U. S. 715, 725 (1966), that a federal court may exercise supplemental jurisdiction over the state claim so long as it "derive[s] from" the same "nucleus of op-erative fact" as the federal one. The Gibbs Court reasoned that when the two claims are so closely related, they make up "but one constitutional 'case' "; and the Court presumed that Congress wanted in that situation to confer jurisdic-tion up to the Constitution's limit. Ibid. (quoting U. S. Const., Art. III, §2, cl. 1); see Exxon Mobil Corp. v. Allapat-tah Services, Inc., 545 U. S. 546, 553 (2005). Congress later confirmed that view, generally codifying Gibbs's supple-mental-jurisdiction rule in 28 U. S. C. §1367 (whose text we will soon consider, see infra, at 7–8). Under that statute, as under Gibbs, jurisdiction over a federal-law claim brings with it supplemental jurisdiction over a state-law claim arising from the same facts. That derivative jurisdiction, though, is to some extent discretionary; §1367 spells out cir-cumstances, again derived from Gibbs, in which a federal court may decline to hear a state claim falling within the statute's bounds. See §1367(c); Gibbs, 383 U. S., at 726–727.
And yet one more preparatory point: If a statute confers federal jurisdiction over a suit, not only the plaintiff but also the defendant can get it into federal court. Take the "arising under" statute: It grants federal district courts "original jurisdiction" over cases presenting a federal ques-tion. §1331; see §1332 (similarly providing "original juris-diction" over diversity suits). The plaintiff may avail her-self of that jurisdiction (and of the opportunity §1367 affords to add supplemental state claims); but she also may file her suit in state court. If she takes the latter route, another statute then gives the defendant an option. Be-cause the case falls within the federal courts' "original ju-risdiction," the defendant may "remove[ ]" it from state to federal court. §1441(a). And there the case (including sup-plemental state claims) usually remains. Except that "[i]f at any time before final judgment it appears that the dis-trict court lacks subject matter jurisdiction," the case must be "remanded" to state court. §1447(c). That is because, to return to where we started, federal courts are courts of lim-ited jurisdiction: When they do not have (or no longer have) authorization to resolve a suit, they must hand it over.
