Article III, Section 2, Clause 1:
The Judicial Power shall extend to all Cases, in Law and Equity, arising under this Constitution, the Laws of the United States, and Treaties made, or which shall be made, under their Authority;—to all Cases affecting Ambassadors, other public Ministers and Consuls;—to all Cases of admiralty and maritime Jurisdiction; to Controversies to which the United States shall be a Party;—to Controversies between two or more States; between a State and Citizens of another State; between Citizens of different States,—between Citizens of the same State claiming Lands under Grants of different States, and between a State, or the Citizens thereof, and foreign States, Citizens or Subjects.
In addition to the other justiciability doctrines discussed above, the Supreme Court's doctrine on mootness imposes another limitation on justiciability derived from Article III's case-or-controversy requirement 1 on the federal courts' jurisdiction to resolve disputes. 2
It has long been settled that a federal court has no authority 'to give opinions upon moot questions;' 3 that is,
when the issues presented are no longer 'live' or the parties lack a cognizable interest in the outcome. 4
An actual controversy must exist not only at the time the complaint is filed, but through all stages of the litigation. 5 Thus,
if an intervening circumstance deprives the plaintiff of a 'personal stake in the outcome of the lawsuit' at any point during litigation, the action can no longer proceed and must be dismissed as moot. 6 The Supreme Court has justified the mootness doctrine on the ground that it
ensures that the Federal Judiciary confines itself to its constitutionally limited role of adjudicating actual and concrete disputes, the resolutions of which have direct consequences on the parties involved. 7
According to the Supreme Court,
a case that becomes moot at any point during the proceedings is  8 Because mootness is a jurisdictional limitation, a federal court can—and indeed must—dismiss a moot case even if none of the parties ask the court to do so. 9 A question about mootness may, in other words, arise at any time during the lifespan of a case, even on appeal. 10 In this respect, mootness
no longer a and is outside the jurisdiction of the federal courts.
Controversy for purposes of Article III,
bears close affinity to the other justiciability doctrines derived from Article III of the Constitution, 11 including standing 12 and the prohibition against advisory opinions. 13 To the extent that the mootness doctrine regulates
the appropriate timing of judicial intervention, 14 mootness serves as the converse of the ripeness doctrine, 15 which restrains the judiciary from adjudicating a case before it develops into a live dispute.
The Supreme Court has steadily developed the substantive and procedural aspects of the mootness doctrine over the course of nearly a century and a half. The Court has ultimately settled on the following formulation of the doctrine:
If an intervening circumstance deprives the plaintiff of a 'personal stake in the outcome of the lawsuit' at any point during litigation, then—subject to certain exceptions analyzed below—
the action can no longer proceed and must be dismissed as moot. 16