Federal Diversity Jurisdiction: Complete Diversity, Entity Citizenship, Amount in Controversy, CAFA, Removal, and Erie

Diversity jurisdiction is the only major federal grant where the fatal defect is usually a fact nobody bothered to check. Federal-question cases fail on doctrine. Diversity cases fail on corporate records: one member of a three-tier LLC turns out to be domiciled in the wrong state, and years of litigation becomes a nullity. The Seventh Circuit has vacated a jury verdict and directed counsel to absorb the cost over exactly that omission.

The doctrine has three moving parts that fail independently. Citizenship must be complete, determined by rules that differ radically by entity form. The amount in controversy must exceed $75,000, judged by a forgiving standard that still has teeth in aggregation cases. And once the case is properly in federal court, 28 U.S.C. § 1652 and the Erie line decide whose law supplies the rule of decision — frequently the whole reason anyone fought about the forum.

This guide covers the tracing exercise that determines entity citizenship, the aggregation and CAFA rules, the time-of-filing rule and the narrow cures the Supreme Court has allowed, removal mechanics, and the Erie/Klaxon framework. It also traces the two clean instances where the Court reversed itself here: the corporate-citizenship cases of 1809 and 1844, and the Zahn-to-Allapattah line.

Contents

• The statutory grant
• Complete diversity is a statute, not a command
• Citizenship by entity type
• The LLC tracing trap
• Amount in controversy and aggregation
• CAFA
• The time-of-filing rule and its limits
• Removal mechanics
• Erie and the rule of decision
• Choice of law and transfer
• Judicially created exceptions
• Practice checklist
• Frequently asked questions

The statutory grant

28 U.S.C. § 1332 does more distinct work than its reputation suggests, and a brief citing "§ 1332" without identifying the operative subsection is usually a sloppy brief.

Two of these are quietly outcome-determinative. Section 1332(c)(2) means a wrongful-death case cannot be steered into federal court by appointing an out-of-state administrator — the appointment buys nothing. And the § 1332(c)(1) proviso deems a liability insurer sued directly, without joining the insured, a citizen of the insured's state as well as its own, which defeats diversity in most direct-action cases.

The threshold has moved repeatedly — $10,000 from 1958, $50,000 from 1988, and "exceeds the sum or value of $75,000" since 1996. It excludes interest and costs but includes properly pleaded punitive damages and, in most circuits, attorney's fees recoverable as an element of the claim.

Alienage has its own traps. A "citizen or subject of a foreign state" does not include a stateless person, and since 2011 § 1332(a)(2) expressly excludes a permanent resident alien domiciled in the same State as the opposing party. Section 1332(a)(3) is the only subsection tolerating aliens on both sides, and only where a diverse state citizen also appears on each side.

Complete diversity is a statute, not a command

Strawbridge v. Curtiss decided in 1806 that when the statute speaks of a controversy between a citizen of one State and a citizen of another, every plaintiff must be diverse from every defendant. Chief Justice Marshall's opinion is four paragraphs and contains no constitutional analysis. It is a reading of the Judiciary Act's words, and the distinction has consequences: Congress can and does legislate below it.

State Farm Fire & Casualty Co. v. Tashire is the cleanest demonstration. Statutory interpleader under 28 U.S.C. § 1335 requires only that two or more adverse claimants be of diverse citizenship, and the Court held that minimal-diversity standard constitutionally sufficient. The same logic underwrites CAFA's § 1332(d)(2), the multiparty-multiforum grant in 28 U.S.C. § 1369, and federal interpleader under Rule 22. When a defendant suggests minimal diversity is constitutionally suspect, Tashire is the answer.

In practice, diversity must exist between opposing parties, aligned by real interest rather than caption. Co-parties may share citizenship freely. A single non-diverse party on the other side is fatal, however small their stake, unless they are dispensable under Rule 19 and can be dropped under Rule 21. And Rule 82 forecloses the argument that the Rules expand jurisdiction.

28 U.S.C. § 1359 polices the obvious workaround, denying jurisdiction where a party "by assignment or otherwise, has been improperly or collusively made or joined to invoke the jurisdiction." It reaches assignments to diverse nominal plaintiffs and jurisdiction-creating appointments. It does not reach the reverse maneuver — a plaintiff who joins a genuine non-diverse defendant to stay in state court is outside § 1359, and the defendant's only answer is fraudulent joinder, which requires showing no possibility of recovery against the resident defendant.

Citizenship by entity type

There is no unified rule. Congress defined citizenship for corporations and said nothing about anything else, and the Court has filled the gap by refusing to extend the corporate rule past the word "corporation."

Natural persons. Domicile, not residence, and the two come apart constantly. Mas v. Perry remains the best teaching case: a Mississippi-domiciled graduate student and her French husband sued their Louisiana landlord for installing a two-way mirror in their bedroom. The Fifth Circuit held that Mrs. Mas, though living in Louisiana, had not acquired a Louisiana domicile because she lacked the intent to remain indefinitely — a student's residence carries no presumption of change. The presumption runs the other way: an established domicile continues until the party is shown to have taken up residence elsewhere with intent to remain, and the burden rests on whoever asserts the change.

The dangerous corollary comes from Mr. Mas's side of the case. His French citizenship supported alienage jurisdiction — but a United States citizen domiciled abroad is a citizen of no State. They cannot invoke § 1332(a)(1) for lack of state citizenship, and cannot invoke § 1332(a)(2) because they are not an alien. Their presence on either side defeats diversity entirely, and nothing in a complaint pleading "residence" reveals them.

Corporations. Section 1332(c)(1) gives dual citizenship: state of incorporation and principal place of business. For decades the second prong produced a circuit-by-circuit mess of total-activities and business-activities tests. Hertz Corp. v. Friend ended that in 2010, unanimously adopting the nerve center test — "the place where a corporation's officers direct, control, and coordinate the corporation's activities," which "should normally be the place where the corporation maintains its headquarters — provided that the headquarters is the actual center of direction, control, and coordination." The Court rejected the Ninth Circuit rule that had made Hertz a California citizen because California generated the plurality of its revenue. Justice Breyer's reason was administrability. A mail drop is disregarded "if the record reveals attempts at manipulation," and the burden rests on the party invoking jurisdiction.

Central West Virginia Energy Co. v. Mountain State Carbon, LLC applied Hertz one layer down. The defendant LLC's citizenship came from its corporate member, whose nerve center was Dearborn, Michigan — where seven of eight officers sat — rather than Wheeling, West Virginia, site of its plant and one vice president. And a parent's citizenship is not the subsidiary's, in either direction: Pyramid Securities Ltd. v. IB Resolution, Inc. rejected attribution of a Cayman subsidiary's citizenship to its Arizona-incorporated, D.C.-headquartered parent even though the parent was sued solely for the subsidiary's acts on a veil-piercing theory, because jurisdictional analysis is not veil-piercing and the statute "suggests no attribution rule in either case." The court then held the subsidiary not a required party under Rule 19 — which mattered, since joining that Cayman entity would have destroyed diversity with the Cayman plaintiff.

A genuine self-overruling. Bank of the United States v. Deveaux held in 1809 that a corporation is not itself a citizen and that courts must look through to the shareholders. Because a corporation "certainly is not a citizen," jurisdiction depended on the "character of the individuals who compose the corporation" — so a corporation with a shareholder in the opposing party's state could never sue in diversity. Thirty-five years later Louisville, Cincinnati & Charleston Rail-Road Co. v. Letson abandoned that rule outright, holding a corporation chartered by a State and doing business there "is to be deemed to all intents and purposes as a person, although an artificial person," and a citizen of its chartering State regardless of its shareholders. Congress codified the result and added the principal-place-of-business prong in 1958.

Deveaux's look-through instinct survives everywhere except corporations, and Hoagland v. Sandberg, Phoenix & von Gontard, P.C. marks the boundary. Judge Posner held that a professional corporation is a corporation for § 1332(c)(1), so a Missouri-incorporated, Missouri-headquartered law firm was a Missouri citizen despite three of its twenty-two shareholders being Illinois citizens: "The statute states flatly that a 'corporation' is a citizen of the state in which it is incorporated and also the state in which its principal place of business is located. The word is not qualified." Had the firm been an LLP or LLC, those three shareholders would have destroyed diversity and the malpractice judgment would have been vacated.

Unincorporated entities. Carden v. Arkoma Associates is controlling and the source of most modern risk. An Arizona limited partnership sued Louisiana citizens, and the Court held 5–4 that the citizenship of the limited partners — passive investors with no control — counted too. Every partner's citizenship is attributed to the partnership, because the entity is not a citizen in its own right and the Court would not invent entity citizenship for a form Congress had not addressed.

Carden rests on United Steelworkers of America v. R. H. Bouligny, Inc., which in 1965 refused to give a labor union entity citizenship even though it had a national identity and sued in its own name. The Court acknowledged the anomaly and left the fix to Congress: "whether unincorporated labor unions ought to be assimilated to the status of corporations for diversity purposes is a matter of policy for Congress." Congress never acted, which is why every LLC case begins with a membership audit.

Trusts turn on who is suing. Where a trustee sues in their own right with real and substantial control over the assets, the trustee's citizenship controls and beneficiaries are irrelevant — the rule of Navarro Savings Association v. Lee (1980). Where the party is the trust itself as an artificial entity, Carden applies and the beneficial owners' citizenship controls, per Americold Realty Trust v. Conagra Foods (2016). GBForefront, L.P. v. Forefront Management Group, LLC had to remand because the record contained the trust instrument for only one of five trusts that were limited partners of a limited partner of the plaintiff partnership.

The LLC tracing trap

Every court of appeals to consider the question applies Carden to the limited liability company: an LLC takes the citizenship of every member. Its state of organization is irrelevant; so is its principal place of business. And because members are frequently themselves LLCs, partnerships, or trusts, the trace continues through however many tiers exist until it reaches natural persons and corporations.

Belleville Catering Co. v. Champaign Market Place, L.L.C. is the case every litigator should know. A case was tried to a jury verdict on the assumption that the defendant LLC was an Illinois citizen because it was organized in Illinois. On appeal, Judge Easterbrook discovered that one member was a corporation with its principal place of business in Illinois — the plaintiff's state — so there had never been jurisdiction. The court vacated the judgment, remanded with instructions to dismiss, and directed that counsel bear the cost: because the loss traced to "counsel's failure to ascertain the basis of federal jurisdiction," the attorneys were to litigate in state court without charging their clients for the wasted federal trial. The operative instruction is a checklist item — the citizenship of an LLC is that of its members, and the rule requires tracing citizenship through however many layers of members there may be.

The other decisions show the same failure from different angles. Hoagland shows how narrowly the same firm escaped by having chosen the professional-corporation form; the Seventh Circuit still had to order supplemental jurisdictional briefing after full merits argument, because "as happens all too often when a suit comes into the federal courts by removal, so that the original pleadings did not specify a basis for federal jurisdiction, the case came to us without adequate specification of the citizenship of the parties." Central West Virginia Energy shows the trace resolved only on appeal after a Hertz fight, GBForefront shows it running four tiers deep with trusts at the bottom, and Pyramid Securities shows that the problem cannot be solved by attributing an affiliate's citizenship to a party.

Two operational points follow. Membership must be fixed as of the date of filing — or, for removed cases, both the date the state action commenced and the date of removal. And use Rule 7.1(a)(2): since the 2022 amendment, every party in a diversity case must file a statement identifying the citizenship of every person whose citizenship is attributed to it. That disclosure exists because of Belleville Catering, and it is the cheapest way to force the issue before anyone invests in the merits.

Amount in controversy and aggregation

The standard is generous to the pleader. The sum claimed in good faith controls, and dismissal is warranted only where it appears to a legal certainty that the claim is really for less — the rule of St. Paul Mercury Indemnity Co. v. Red Cab Co. (1938). Post-filing events reducing the claim do not oust jurisdiction; a plaintiff who recovers $40,000 on a good-faith $200,000 claim keeps the judgment, though § 1332(b) permits denying costs and even imposing them.

Legal certainty is real but narrow. It is met where a statute or contract caps recovery below the threshold, where a liquidated sum is arithmetically insufficient, or where state law forecloses the damages category that gets the plaintiff over the line. It is not met by a defendant's confident view that the case is worth less.

Aggregation is harder:

• One plaintiff against one defendant may aggregate all claims, however unrelated.
• Multiple plaintiffs may aggregate only where they assert a single title or right in which they have a common and undivided interest. Separate and distinct claims cannot be added.
• One plaintiff against multiple defendants may aggregate only as to claims of joint liability.
• Equitable relief is valued by the object of the litigation.

Snyder v. Harris held in 1969 that the 1966 revision of Rule 23 did not change the aggregation rule, because the Rules cannot extend or limit jurisdiction. Zahn v. International Paper Co. extended Snyder to the harder case four years later: even where the named plaintiffs satisfied the amount, class members whose individual claims fell short had to be dismissed. That made most consumer classes unmaintainable in diversity.

The reversal. Exxon Mobil Corp. v. Allapattah Services, Inc. overruled Zahn's holding in 2005 on the strength of 28 U.S.C. § 1367. Section 1367(a) grants supplemental jurisdiction over all claims forming part of the same case or controversy, including claims joining additional parties, and § 1367(b) withholds jurisdiction only over claims by plaintiffs against persons joined under Rules 14, 19, 20, and 24. It says nothing about claims by plaintiffs joined under Rule 20 or Rule 23 against the original defendant. So where one plaintiff clears $75,000, § 1367 supplies jurisdiction over co-plaintiffs who do not.

Two cautions. Allapattah concerns the amount requirement only — complete diversity is untouched, so one non-diverse plaintiff still destroys the whole action while one under-threshold plaintiff does not. And § 1367(c) discretion survives. A corollary: there must be original jurisdiction over at least one claim judged without reference to § 1367, so if no plaintiff clears the threshold there is nothing to be supplemental to.

CAFA

The Class Action Fairness Act of 2005 added § 1332(d) and 28 U.S.C. § 1453 to move large interstate class actions into federal court, relaxing every element of ordinary diversity at once.

CAFA also reaches "mass actions" under § 1332(d)(11) — suits in which the monetary claims of 100 or more persons are proposed to be tried jointly — and carves out securities and internal-corporate-affairs claims, the mandatory local-controversy and home-state exceptions in § 1332(d)(4), and the discretionary factors in § 1332(d)(3).

Standard Fire Insurance Co. v. Knowles closed the obvious escape hatch. A class representative stipulated the class would seek less than $5 million, and the district court remanded. A unanimous Court reversed: a named plaintiff's stipulation cannot bind absent class members before certification, so it "does not reduce the value of the putative class members' claims." The court must ignore it and determine the amount as if certification would be granted.

Dart Cherokee Basin Operating Co. v. Owens fixed the removal pleading standard. A notice need only plausibly allege the amount; evidence is required only when the plaintiff contests it or the court questions it, at which point § 1446(c)(2)(B) requires a preponderance finding. The Court also rejected the antiremoval presumption many circuits had applied: "no antiremoval presumption attends cases invoking CAFA, which Congress enacted to facilitate adjudication of certain class actions in federal court."

Dudley v. Eli Lilly & Co. shows that burden in operation. The Eleventh Circuit affirmed remand of an unpaid-incentive-compensation class action because Lilly's evidence — affidavits giving the number of eligible sales representatives and a range of potential payments — did not correlate to the compensation categories the complaint actually put at issue. A removing defendant "is not required to prove the amount in controversy beyond all doubt or to banish all uncertainty about it," and the question is what is in controversy rather than what the plaintiff will recover, but speculation without guideposts is not a preponderance. Dart removed the presumption, not the burden.

Mississippi ex rel. Hood v. AU Optronics Corp. held unanimously that a State attorney general's parens patriae antitrust suit is not a mass action, even though the State sought restitution for many consumers. "Claims of 100 or more persons" means claims of 100 or more named plaintiffs, and the State was the only one. The Court declined to look through the caption to the real parties in interest — now the standard defense against CAFA removal of state enforcement actions.

Home Depot U.S.A., Inc. v. Jackson held in 2019 that a third-party counterclaim defendant may not remove — neither under § 1441(a)'s "the defendant or the defendants" nor under § 1453(b)'s "any defendant." Home Depot had been brought in by a consumer's class counterclaim against the original plaintiff bank. The Court read "defendant" in both provisions to mean the party sued by the original plaintiff, since § 1453(b) changed who must consent and which eligible defendants may remove, not the threshold definition. The decision has made counterclaim class actions a deliberate plaintiff-side tactic.

Johnson v. Advance America is the clearest circuit illustration, and it rewards careful class drafting. South Carolina plaintiffs defined their class to include only citizens of South Carolina and named only South Carolina-citizen defendants, the lead defendant being a citizen of both Delaware and South Carolina. The Fourth Circuit affirmed remand because the removing defendant could not show that any class member was a citizen of a State "different from" it under § 1332(d)(2)(A): a dual citizen is a citizen of both States, and a class limited to South Carolina citizens excludes former residents who moved away. The takeaway runs both ways — a class defined by citizenship rather than by transaction can defeat minimal diversity, and a defendant should attack that definition rather than concede it.

The time-of-filing rule and its limits

Jurisdiction is measured when the complaint is filed, and nothing afterward changes the answer. Four decisions appear inconsistent until you separate what changed.

Grupo Dataflux v. Atlas Global Group, L.P. states the rule and refuses to soften it. A Texas limited partnership sued a Mexican corporation; two of its partners were Mexican citizens at filing, so alienage failed — aliens on both sides. After a $6.7 million verdict but before judgment those partners withdrew, making the partnership wholly diverse. The Court held 5–4 that a post-filing change in a party's own citizenship composition could not cure the defect, and vacated the verdict. Justice Scalia called the rule "hornbook law," valuable for avoiding "the expense and delay of litigating jurisdiction."

Caterpillar Inc. v. Lewis is the cure that works. A case was removed while a non-diverse defendant remained, making removal improper; that defendant settled out before trial, so complete diversity existed at judgment. A unanimous Court held vacatur unnecessary: "once a diversity case has been tried in federal court . . . considerations of finality, efficiency, and economy become overwhelming." The distinction from Grupo Dataflux is precise — dropping a jurisdictional spoiler cures, while a continuing party's own change of citizenship does not.

Newman-Green, Inc. v. Alfonzo-Larrain supplies the appellate version. An Illinois corporation sued a Venezuelan corporation and five guarantors, one a U.S. citizen domiciled in Venezuela — a citizen of no State. The Court held that a court of appeals may itself dismiss a dispensable non-diverse party under Rule 21 rather than remanding, preserving the judgment against the rest, while cautioning that the power be used "sparingly" after weighing prejudice.

Freeport-McMoRan, Inc. v. K N Energy, Inc. completes the picture. Diversity existed at filing; the plaintiff then assigned its contract interest to a limited partnership sharing the defendant's citizenship and joined it as co-plaintiff. The Court held per curiam that post-filing joinder of a non-diverse party did not destroy jurisdiction, because diversity is assessed when the action is filed. The symmetry is exact: post-filing events neither create nor destroy, so the doctrine cuts for whoever had it right at filing.

For removed cases the measurement doubles. Diversity must exist both when the state action was commenced and when the notice of removal is filed.

Removal mechanics

The forum-defendant rule. Section 1441(b)(2) bars diversity removal if any defendant "properly joined and served" is a citizen of the State where the action was brought. This is a procedural defect, not jurisdictional, so it must be raised within 30 days under § 1447(c) or it is forfeited. The "properly joined and served" language has produced the contested snap-removal practice — a non-forum defendant removing before the forum defendant is served.

Clocks. Section 1446(b)(1) gives 30 days from receipt of the initial pleading, and § 1446(b)(3) opens a new window when an amended pleading, motion, order, or other paper first makes the case removable. Section 1446(b)(2) requires the consent of all properly joined and served defendants, each with its own 30 days from its own service. Section 1446(c)(1) imposes a hard one-year limit on diversity removals from commencement, subject only to a finding of bad faith — and § 1446(c)(3)(B) makes deliberate nondisclosure of the amount in controversy evidence of it.

Non-removable claims. 28 U.S.C. § 1445 makes several categories non-removable regardless of diversity: FELA actions, Jones Act suits by operation of the FELA incorporation, workers' compensation claims under a State's compensation law, and Violence Against Women Act civil claims. The compensation bar is the one most often encountered, and a removal sweeping in a comp claim invites a fee award under § 1447(c).

Wisconsin Department of Corrections v. Schacht addresses a removable case containing a non-removable claim. A § 1983 complaint joined claims against a State barred by the Eleventh Amendment, and the Court held unanimously that the presence of a claim the federal court cannot adjudicate does not defeat removal of the whole case; the district court takes it, dismisses the barred claim, and proceeds.

Breuer v. Jim's Concrete of Brevard, Inc. sets the interpretive default. The FLSA provides that an action "may be maintained . . . in any Federal or State court of competent jurisdiction," and the plaintiff argued this barred removal. A unanimous Court disagreed: § 1441(a) permits removal "except as otherwise expressly provided by Act of Congress," and an express prohibition means what it says. The presumption favors removability, and a party resisting it needs a statute like § 1445, not an inference.

Powerex Corp. v. Reliant Energy Services, Inc. governs review of remand orders. Section 1447(d) bars review except in cases removed under §§ 1442 and 1443, and the bar reaches remands on the grounds specified in § 1447(c). Powerex held that when a district court characterizes its remand as based on lack of subject-matter jurisdiction, the characterization is unreviewable even if substantively wrong, so long as it was colorable — so a plaintiff who wins a jurisdictional remand usually keeps it. CAFA is the exception: § 1453(c) authorizes a court of appeals to accept an appeal from a CAFA remand, which is how Johnson, Dudley, and Dart Cherokee reached appellate courts at all.

Royal Canin U.S.A., Inc. v. Wullschleger, decided in January 2025, addresses post-removal amendment. A plaintiff who amends after removal to delete every federal claim strips the district court of both federal-question and § 1367 supplemental jurisdiction, because § 1367(a) requires a live anchor claim. Royal Canin is a federal-question case but matters here for the contrast: the maneuver does not work in diversity, since under Freeport-McMoRan an amendment reducing the claimed amount or adding a non-diverse party after removal does not defeat jurisdiction that existed at filing and removal.

Lincoln Property Co. v. Roche is the case for what a removing defendant need not do. Virginia homeowners sued a Texas partnership over mold damage, and the Fourth Circuit — in the decision reported as Roche v. Lincoln Property Co. — held removal improper because the defendant had not negated the existence of an affiliated Virginia entity that might have owned the property. The Supreme Court reversed unanimously: "a defendant seeking removal need not negate the existence of a potential defendant whose presence in the action would destroy diversity." Only the real and substantial parties count, and the plaintiff chooses whom to sue. The corollary for plaintiffs is equally clear — naming the local affiliate defeats removal.

Kokkonen v. Guardian Life Insurance Co. of America supplies both the background presumption and a trap at the end of the case: "It is to be presumed that a cause lies outside this limited jurisdiction, and the burden of establishing the contrary rests upon the party asserting jurisdiction." Kokkonen held that a district court has no inherent ancillary jurisdiction to enforce a settlement whose terms were not incorporated into the dismissal order. A stipulated dismissal under Rule 41(a) ends the case, and the settlement becomes an ordinary state-law contract. Recite the terms in the dismissal order or retain jurisdiction expressly — otherwise, in a case settling under $75,000, there is no federal forum for enforcement at all.

Erie and the rule of decision

Getting into federal court settles the forum, not the law. 28 U.S.C. § 1652 — the Rules of Decision Act, essentially unchanged since 1789 — provides that "the laws of the several states . . . shall be regarded as rules of decision in civil actions in the courts of the United States, in cases where they apply."

The overruling. Swift v. Tyson read "the laws of the several states" in 1842 to mean state statutes and local usages, not state common law, leaving federal courts free to find general commercial law for themselves. For ninety-six years they did. Erie Railroad Co. v. Tompkins overruled Swift in 1938 on several grounds at once: its historical premise was wrong; the regime produced "grave discrimination by non-citizens against citizens" through forum shopping — the plaintiff sued in New York federal court precisely to escape Pennsylvania's rule that a trespasser on railroad tracks could recover only for wanton negligence; and, most consequentially, "there is no federal general common law," so the Swift doctrine invaded rights reserved to the States. That constitutional footing is why parties cannot contract around Erie.

Guaranty Trust Co. v. York supplied the first test in 1945 — the outcome-determinative standard, requiring a federal court to apply a state statute of limitations in an equitable action because "the outcome of the litigation in the federal court should be substantially the same . . . as it would be if tried in a State court." Taken literally, that would state-ify almost everything. Byrd v. Blue Ridge Rural Electric Cooperative, Inc. limited York in 1958 with countervailing federal interests: South Carolina practice assigned a workers'-compensation immunity question to the judge, federal practice gave fact questions to the jury, and the federal practice controlled because the state rule was not bound up with state-created rights and the federal interest in the jury's role outweighed the risk of a different outcome. Cite Byrd when the state rule is judicial administration rather than substance.

Hanna v. Plumer then split the analysis in two, the most important structural feature of modern Erie practice. Where a Federal Rule directly collides with state law — there, Rule 4's provision for leaving process with a spouse at the defendant's dwelling versus Massachusetts' requirement of in-hand service on an executor — the question is not the York outcome test. It is whether the Rule is valid under the Rules Enabling Act, 28 U.S.C. § 2072, which authorizes rules of "practice and procedure" that do not "abridge, enlarge or modify any substantive right." A valid Rule applies, period. Only where no Federal Rule covers the point does the court reach Erie/York, restated as the twin aims of discouraging forum shopping and avoiding inequitable administration of the laws.

Walker v. Armco Steel Corp. shows how narrowly the Court reads "direct collision." Oklahoma law required actual service to toll the limitations period; Rule 3 says an action is commenced by filing. The Court found no conflict — Rule 3 governs the internal timetable of the Federal Rules and was never meant to displace a state tolling rule forming part of the State's substantive limitations policy. The state rule applied and the claim was time-barred. Walker is why a party should argue "no direct collision" before arguing Rules Enabling Act invalidity.

Stewart Organization, Inc. v. Ricoh Corp. extended the Hanna logic to federal statutes. Alabama law treated forum-selection clauses as unenforceable; 28 U.S.C. § 1404(a) authorizes transfer for convenience and in the interest of justice. Section 1404(a) controlled as a valid exercise of Congress's power over federal procedure, making the clause a weighted factor in the transfer calculus rather than a nullity.

Gasperini v. Center for Humanities, Inc. shows accommodation at its most delicate. New York's CPLR 5501(c) directed appellate review of damages awards that "deviate materially" from reasonable compensation; federal practice reviewed for abuse of discretion. The Court held the state standard substantive enough to apply but directed the district court to apply it on a new-trial motion, with ordinary abuse-of-discretion review on appeal — both interests served, neither rule applied as written.

Shady Grove Orthopedic Associates, P.A. v. Allstate Insurance Co. is the modern fault line. New York's CPLR 901(b) barred class actions seeking statutory penalties; the plaintiff sought certification under Rule 23. Five Justices agreed Rule 23 applied, but not on why. Justice Scalia, for four, read Rule 23 as categorically answering whether a class may be certified and held that validity under § 2072 turns only on whether the Rule "really regulates procedure," making the state law's substantive purpose irrelevant. Justice Stevens, supplying the fifth vote, insisted a Federal Rule can be inapplicable where it would displace a state rule "so intertwined with a state right or remedy that it functions to define the scope of the state-created right," but found CPLR 901(b) not so intertwined. Justice Ginsburg, dissenting for four, would have read Rule 23 narrowly to avoid the conflict — the Walker move. Because Justice Stevens concurred on the narrowest ground, most circuits treat his opinion as controlling, so the § 2072 analysis retains a substantive-entwinement inquiry that four Justices rejected. Expect any serious Erie fight over a Federal Rule to be a fight about which Shady Grove opinion governs.

Semtek International Inc. v. Lockheed Martin Corp. closes the loop. A California federal court dismissed a claim as time-barred; the plaintiff refiled in Maryland, where the longer period had not run. A unanimous Court held that the preclusive effect of a federal diversity judgment is governed by federal common law, but that federal common law ordinarily adopts the law of the State where the rendering court sits — and that Rule 41(b)'s "adjudication upon the merits" language means only that the dismissal bars refiling in the same court, not that it is claim-preclusive everywhere.

Choice of law and transfer

Erie tells the federal court to apply state law. It does not say which State's.

Klaxon Co. v. Stentor Electric Manufacturing Co. answered that in 1941: a federal court sitting in diversity applies the conflict-of-laws rules of the State in which it sits. The Court rejected the view that a federal court could exercise independent judgment on the choice-of-law question, reasoning that "the proper function of the Delaware federal court is to ascertain what the state law is, not what it ought to be," and that any other rule would reintroduce the forum shopping Erie eliminated. So a choice-of-law brief in federal court is a brief about forum-state conflicts doctrine, and selecting a district is selecting a conflicts regime.

Transfer carries the transferor's law. Van Dusen v. Barrack held in 1964 that a § 1404(a) transfer effects a change of courtrooms, not a change of law: the transferee court applies the choice-of-law rules the transferor would have applied. Otherwise a defendant could, by moving the case, strip the plaintiff of the law they were entitled to when they filed in a proper forum.

Ferens v. John Deere Co. extended Van Dusen to a transfer sought by the plaintiff, and the result is startling enough to state plainly. A Pennsylvania plaintiff whose tort claim was time-barred at home filed in Mississippi, which then had a six-year period and applied its own limitations law, then moved to transfer to Pennsylvania for convenience. The Court held 5–4 that Mississippi's limitations law traveled with the case, so the plaintiff litigated at home under a period his home forum would never have given him — Van Dusen's rule could not sensibly depend on which party moved. Ferens is why a defendant facing a plaintiff's transfer motion should consider forum non conveniens rather than acquiescing.

Atlantic Marine Construction Co. v. United States District Court settled forum-selection mechanics in 2013. A valid clause naming another federal district is enforced through § 1404(a), not Rule 12(b)(3) or § 1406 — venue in the filed district is proper if the venue statute's criteria are met, regardless of the clause. But the clause transforms the calculus: the plaintiff's choice of forum "merits no weight," the plaintiff bears the burden of showing transfer is unwarranted, the private-interest factors weigh entirely for the preselected forum, and — critically — a transfer enforcing a forum-selection clause does not carry the transferor's choice-of-law rules, because the Van Dusen/Ferens rationale of protecting a legitimate forum choice does not protect a plaintiff who breached the clause. That last point is the one most often missed.

Great Lakes Insurance SE v. Raiders Retreat Realty Co. added the maritime overlay in 2024. A marine policy contained a New York choice-of-law provision, and the insured argued Pennsylvania's public policy on insurance bad faith should override it. The Court held 9–0 that choice-of-law provisions in maritime contracts are presumptively enforceable as a matter of federal maritime law, and that a State's contrary public policy is not among the narrow exceptions. Because many marine-insurance disputes arrive under § 1332, Great Lakes means the Klaxon reflex is wrong in those cases: where federal maritime law supplies the rule, forum-state conflicts doctrine does not.

Judicially created exceptions

Two categories satisfy § 1332 on paper and are still dismissed. Both are judge-made, both rest on the historical understanding of the 1789 grant, and both have been narrowed by the Court itself.

Domestic relations. Ankenbrandt v. Richards both preserved and confined the exception in 1992. A mother sued her ex-husband and his companion in diversity for tortiously abusing her daughters, and the Fifth Circuit dismissed. The Supreme Court reversed. Justice White located the exception in statutory history — the 1789 grant covered suits at common law or in equity, and English chancery practice did not include divorce or alimony — and held it "divests the federal courts of power to issue divorce, alimony, and child custody decrees" and nothing more. A tort claim between family members is none of those. Burford abstention might occasionally apply, but that is discretionary, not jurisdictional. The practical reading: plead damages, not status. A claim to enforce a support order or divide marital property draws the exception; a claim for money for a completed wrong does not.

Probate. Marshall v. Marshall narrowed the probate exception sharply in 2006. Justice Ginsburg confined it to probating or annulling a will, administering a decedent's estate, and disposing of property in the custody of a state probate court. A claim for tortious interference with an expected inter vivos gift was none of those — it was an in personam damages claim against another individual — so jurisdiction existed. The Court rejected outright the lower courts' expansion of the exception, through the "interference" language of Markham v. Allen, into a general bar on anything touching probate.

Manufactured diversity and § 1369. Section 1359 remains the backstop against collusive assignments and nominal-party devices, but only against devices that create jurisdiction — joining a genuine non-diverse defendant to defeat it is legitimate, as Lincoln Property and Johnson v. Advance America confirm. And 28 U.S.C. § 1369, added in 2002, is a minimal-diversity grant for a single accident at a discrete location killing at least 75 natural persons, with a mandatory abstention provision where the substantial majority of plaintiffs and the primary defendants are local. Like CAFA and § 1335 interpleader, it exists because Strawbridge was statutory.

Practice checklist

1. Trace every entity before filing or removing. Obtain a dated membership or partnership schedule for each LLC and partnership party, and repeat down every tier until the chain reaches natural persons and corporations. Belleville Catering is what happens otherwise, and the cost there fell on counsel.
2. Plead citizenship, not residence. Rule 8(a)(1) requires a short and plain statement of the grounds for jurisdiction, and "resident of" is not one. Allege domicile for individuals, both prongs for corporations, and each member's citizenship for an LLC.
3. Screen for the citizen-of-no-State problem. Any U.S. citizen domiciled abroad — on either side, including as an LLC member three tiers down — defeats diversity entirely.
4. Check § 1332(c)(2) and the direct-action proviso. An out-of-state administrator buys nothing, and a directly sued liability insurer takes the insured's citizenship as well as its own.
5. Test the amount against the aggregation rules. Multiple plaintiffs aggregate only on a common and undivided interest; claims against multiple defendants aggregate only where liability is joint. If one plaintiff clears $75,000, Allapattah carries the rest — on amount only, never on diversity.
6. On CAFA removal, allege plausibly and prepare to prove. Dart Cherokee excuses attaching evidence, but § 1446(c)(2)(B) requires a preponderance showing once contested, and Dudley shows that extrapolation from a partial record will not carry it.
7. Calendar both § 1446 clocks — 30 days from service or from the first paper making the case removable, and the one-year outer limit — and obtain each co-defendant's consent in writing.
8. Confirm § 1441(b)(2) and § 1445 before removing. A forum-defendant violation is procedural and forfeits in 30 days; removing a workers' compensation claim invites a fee award.
9. Cure defects before judgment. Drop a dispensable non-diverse party under Rule 21; Caterpillar then protects the judgment. Grupo Dataflux forecloses the cure where only a continuing party's citizenship changed, and Newman-Green is the last resort on appeal.
10. Run the Erie analysis on every state rule you rely on. If a Federal Rule or federal statute directly answers the question, the fight is § 2072 validity under the competing Shady Grove opinions; if not, it is Hanna's twin aims tempered by Byrd.
11. Brief choice of law as forum-state conflicts law. Klaxon governs, Van Dusen and Ferens make a § 1404(a) transfer carry the transferor's rules, Atlantic Marine makes a clause-enforcing transfer an exception, and Great Lakes displaces the reflex in maritime cases.
12. Preserve enforcement jurisdiction at settlement. Under Kokkonen, recite the terms in the dismissal order or retain jurisdiction expressly.

Frequently asked questions

Is complete diversity required by the Constitution?

No. Strawbridge v. Curtiss construes statutory language, not Article III, and the Court has repeatedly said so. State Farm Fire & Casualty Co. v. Tashire proves it: statutory interpleader under § 1335 requires only minimal diversity among two or more claimants, and that satisfies Article III. Congress used the same freedom for CAFA and § 1369. The corollary is that a court cannot relax complete diversity in an ordinary § 1332(a) case on the theory that Article III would tolerate it — the statute is the ceiling Congress set.

How do I determine the citizenship of an LLC whose members are other LLCs?

Trace every tier. Each member contributes its own citizenship; an LLC or partnership member contributes the citizenship of its members; a corporate member contributes its state of incorporation and nerve center under Hertz; a traditional trust contributes its trustee's citizenship under GBForefront. There is no shortcut and no attribution principle — Pyramid Securities holds that parent and subsidiary citizenships are not interchangeable in either direction. The Rule 7.1(a)(2) disclosure statement is the cheapest way to make opposing parties do the same work.

Does revenue or the largest facility determine a corporation's principal place of business?

No, not since 2010. Hertz Corp. v. Friend rejected the business-activities and total-activities tests for the nerve center — the single place where officers direct, control, and coordinate, normally the headquarters. Revenue concentration, headcount, and plant locations matter only as evidence that a nominal headquarters is a fiction. Central West Virginia Energy is the working example: Dearborn, where the officers sat, not Wheeling, where the plant was.

One of several plaintiffs has a claim worth less than $75,000. Is the case out?

No. Exxon Mobil Corp. v. Allapattah Services held that where at least one plaintiff satisfies the amount, § 1367(a) supplies supplemental jurisdiction over co-plaintiffs who fall short, because § 1367(b) does not carve out claims by plaintiffs joined under Rule 20 or Rule 23 against the original defendant. That overruled Zahn v. International Paper Co. But the holding is confined to the amount requirement — a single non-diverse plaintiff still defeats the entire action, and § 1367(c) discretion remains.

Can a class representative stipulate below $5 million to avoid CAFA?

No. Standard Fire Insurance Co. v. Knowles held unanimously that a pre-certification stipulation cannot bind absent class members and so does not reduce the value of their claims; the court determines the amount as though certification would be granted. Class definition is different. Johnson v. Advance America shows that defining a class by state citizenship, and naming only defendants sharing it, can defeat minimal diversity under § 1332(d)(2)(A).

A non-diverse defendant settled out before trial. Must the judgment be vacated?

No. Caterpillar Inc. v. Lewis holds that a defect existing at removal but cured before judgment does not require vacatur, because finality, efficiency, and economy become overwhelming once the case has been tried. The distinction from Grupo Dataflux v. Atlas Global Group is what changed: dismissing a jurisdictional spoiler cures, while a continuing party's own post-filing change of citizenship does not. If the defect surfaces on appeal, Newman-Green, Inc. v. Alfonzo-Larrain lets the court of appeals itself drop a dispensable non-diverse party.

Whose law applies once the case is in federal court?

The forum State's, including its choice-of-law rules, which may point elsewhere. Erie Railroad Co. v. Tompkins overruled Swift v. Tyson and ended federal general common law; § 1652 requires state law as the rule of decision; and Klaxon requires applying the conflicts doctrine of the State where the court sits. Where a Federal Rule or federal statute directly answers the question, Hanna v. Plumer and Stewart Organization v. Ricoh route the analysis to validity under § 2072 or the Constitution rather than to Guaranty Trust v. York's outcome test. Shady Grove is where that analysis currently fractures.

Can a third-party counterclaim defendant remove a class action under CAFA?

No. Home Depot U.S.A., Inc. v. Jackson held that "defendant" in § 1441(a) and § 1453(b) means the party sued by the original plaintiff. A party brought in only by a defendant's counterclaim may not remove, even if that counterclaim satisfies every CAFA threshold. Section 1453(b) changed which eligible defendants may remove and eliminated unanimity; it did not expand who counts as a defendant.

What is left of the domestic-relations and probate exceptions?

Very little. Ankenbrandt v. Richards confines the domestic-relations exception to issuing divorce, alimony, and child-custody decrees; an intrafamily tort claim is fully within § 1332. Marshall v. Marshall confines the probate exception to probating or annulling a will, administering an estate, and disposing of property in a probate court's custody. In both areas the question is whether you are asking the federal court to issue a decree of status or administer a res, or merely to award money.