In the law of the United States, diversity jurisdiction is a form of subject-matter jurisdiction that gives United States federal courts the power to hear lawsuits that do not involve a federal question. For a federal court to have diversity jurisdiction over a lawsuit, two conditions must be met. First, there must be "diversity of citizenship" between the parties, meaning the plaintiffs must be citizens of different U.S. states than the defendants. Second, the lawsuit's "amount in controversy" must be more than $75,000. If a lawsuit does not meet these two conditions, federal courts will normally lack the jurisdiction to hear it unless it involves a federal question, and the lawsuit would need to be heard in state court instead.

The United States Constitution, in Article III, Section 2, grants Congress the power to permit federal courts to hear diversity cases through legislation authorizing such jurisdiction. The provision was included because the Framers of the Constitution were concerned that when a case is filed in one state, and it involves parties from that state and another state, the state court might be biased toward the party from that state. Congress first exercised that power and granted federal trial circuit courts diversity jurisdiction in the Judiciary Act of 1789. Diversity jurisdiction is currently codified at 28 U.S.C. § 1332, the statute originally enacted on June 25, 1948.

In 1969, the American Law Institute explained in a 587-page analysis of the subject that diversity is the "most controversial" type of federal jurisdiction, because it "lays bare fundamental issues regarding the nature and operation of our federal union."

(a) The district courts shall have original jurisdiction of all civil actions where the matter in controversy exceeds the sum or value of $75,000, exclusive of interest and costs, and is between—

— 28 U.S.C. § 1332.

Mostly, in order for diversity jurisdiction to apply, complete diversity is required, where none of the plaintiffs can be from the same state as any of the defendants. A corporation is treated as a citizen of the state in which it is incorporated and the state in which its principal place of business is located. A partnership or limited liability company is considered to have the citizenship of all of its constituent partners/members. Thus, an LLC or partnership with one member or partner sharing citizenship with an opposing party will destroy diversity of jurisdiction. Cities and towns (incorporated municipalities) are also treated as citizens of the states in which they are located, but states themselves are not considered citizens for the purpose of diversity. U.S. citizens are citizens of the state in which they are domiciled, which is the last state in which they resided and had an intent to remain.

A national bank chartered under the National Bank Act is treated as a citizen of the state in which it is "located". In 2006, the Supreme Court rejected an approach that would have interpreted the term "located" to mean that a national bank is a citizen of every state in which it maintains a branch. The Supreme Court concluded that "a national bank ... is a citizen of the State in which its main office, as set forth in its articles of association, is located". The Supreme Court, however, left open the possibility that a national bank may also be a citizen of the state in which it has its principal place of business, thus putting it on an equal footing with a state-formed corporation. This remains an open question, with some lower courts holding that a national bank is a citizen of only the state in which its main office is located, and others holding that a national bank is also a citizen of the state in which it has its principal place of business.

The diversity jurisdiction statute also allows federal courts to hear cases in which: