## Facts

- A Texas limited partnership filed a state-law action in federal district court against a Mexican corporation, invoking diversity jurisdiction under 28 U.S.C. § 1332.
- At filing, two partners of the partnership were Mexican citizens, and the defendant was a Mexican corporation.
- Because a partnership has the citizenship of each partner, the plaintiff partnership was considered a citizen of Mexico at filing.
- Before trial, the two Mexican partners withdrew from the partnership, leaving only non-Mexican partners.
- A jury returned a verdict for the plaintiff.
- After the verdict but before entry of judgment, the defendant moved to dismiss for lack of subject-matter jurisdiction based on the absence of complete diversity at filing.
- The magistrate judge dismissed for lack of jurisdiction.
- The court of appeals reversed, reasoning that the defect was “cured” before trial by the partners’ withdrawal and was not identified until after the verdict.

## Issues

1. Whether lack of complete diversity at the time of filing may be cured for subject-matter jurisdiction purposes by a post-filing change in an existing party’s citizenship.
2. Whether considerations of finality and efficiency permit a federal court to proceed to judgment when a diversity defect present at filing is later eliminated without dismissal of a party.

## Decision

- The Supreme Court reversed the court of appeals in a 5–4 decision.
- The Court held that a post-filing change in citizenship cannot cure a lack of subject-matter jurisdiction that existed at the time of filing in a diversity action.
- The time-of-filing rule controlled because there was no change in the identity of the parties; only the citizenship of an existing party changed through partner withdrawals.
- The Court distinguished prior precedent allowing cure by dismissal of a dispensable non-diverse party before trial, finding that rationale inapplicable where no party was dismissed.
- Because aliens were on both sides at filing, diversity jurisdiction was absent and dismissal was required.

## Legal Principles

- Diversity jurisdiction is determined by the citizenship of the parties as it existed at the time the complaint was filed.
- A partnership is a citizen of every state or foreign country of which any partner is a citizen.
- Post-filing changes to the citizenship of a party that remains in the case do not create subject-matter jurisdiction where it was absent at filing.
- The limited exception recognized in cases allowing cure of diversity defects applies when a dispensable non-diverse party is dismissed, not when a party’s citizenship changes while the party remains.
- Finality and efficiency do not justify creating a new exception that would permit jurisdiction to rest on later changes in citizenship rather than the filing-date facts.

## Conclusion

The Court required dismissal because complete diversity was lacking when the suit was filed, and later withdrawal of non-diverse partners—without dismissal of any party from the case—could not retroactively supply federal subject-matter jurisdiction.


Grupo Dataflux v. Atlas Glob. Grp., L.P., 541 U.S. 567 (2004)