Case or Controversy Clause
Article III, Section 2, Clause 1 of the Constitution states:
This clause, in addition to setting out the scope of the jurisdiction of the federal judiciary, prohibits courts from issuing advisory opinions, or from hearing cases that are either unripe, meaning that the controversy has not arisen yet, or moot, meaning that the controversy has already been resolved. The earliest expression by the United States Supreme Court of adherence to this requirement came during the presidency of George Washington. Washington sent a letter to the Court asking for their approval should he choose to seek advice from them from time to time on matters that might not come before the Court in a timely manner. Chief Justice John Jay wrote in his response that, although the members of the Court had great confidence in the ability of the president to receive appropriate advice from his executive officers, the Court itself was constitutionally bound not to go beyond its role as an arbiter of judicial questions. The most famous case setting forth the parameters of this requirement is "Muskrat v. United States", 219 U.S. 346 (1911), in which the Court held that when Congress paid the legal bills for both the plaintiffs and the defendant (in this case the U.S. Treasury department, by designation), then there was no real controversy between the parties, and a judgment of the Court would be the equivalent of an advisory opinion. The boundaries of the "case and controversy" clause are open to dispute. For instance, the Court has held that where the controversy between parties has ceased because of a change in facts, it has no jurisdiction. However, where the case or controversy ceases—or, in legal terms, is "mooted"—after a case is filed, the Court may render a decision in the interest of justice. In "Roe v. Wade", for instance, the Court applied the mootness exception for cases "capable of repetition, yet evading review." Justice Harry Blackmun wrote that due to the natural limitation of the human gestation period, issues concerning pregnancy will always come to term before the appellate process is complete. "Roe v. Wade" 410 U.S. 113 (1973). Therefore, the Supreme Court could rule on the constitutionality of an abortion law despite the issue being moot at the time of adjudication. The U.S. Supreme Court observed in "DaimlerChrysler Corp. v. Cuno" (2006): "No principle is more fundamental to the judiciary’s proper role in our system of government than the constitutional limitation of federal-court jurisdiction to actual cases or controversies.” The case-or-controversy requirement of Article III of the constitution requires plaintiffs to establish their standing to sue. Article III standing law is built on separation-of-powers principles. Its purpose is to prevent the judicial process from being used to usurp the powers of the legislative and executive branch of the U.S. federal government. Article III standing requires an injury that is “concrete, particularized and actual or imminent; fairly traceable to the challenged action and redressable by a favorable ruling.” Generally, the clause is taken to mean that a vague, broad injury is not grounds for a federal lawsuit. Relevant cases:
 "Lujan v. Defenders of Wildlife" ("[A person] raising only a generally available grievance about government—claiming only harm to his and every citizen’s interest in proper application of the Constitution and laws, and seeking relief that no more directly and tangibly benefits him than it does the public at large—does not state an Article III case or controversy."), "Allen v. Wright" ("an asserted right to have the Government act in accordance with law is not sufficient, standing alone, to confer jurisdiction on a federal court"), "Diamond v. Charles" (Article III standing "is not to be placed in the hands of ‘concerned bystanders,’ for use as a ‘vehicle for the vindication of value interests.’"), "Arizonans for Official English" ("Nor has this Court ever identified initiative proponents as Article-III-qualified defenders of the measures they advocated."), "Karcher v. May" (Citizens who had standing in their 'public official' roles did not retain standing once they left public office), "Hollingsworth v. Perry" ("We have never before upheld the standing of a private party to defend the constitutionality of a state statute when state officials have chosen not to. We decline to do so for the first time here"), and numerous other cases. The clause does not forbid individual States from granting standing to such parties; it only mandates that federal courts may not do so:
 "The Court does not question [the State's] sovereign right to maintain an initiative process, or the right of initiative proponents to defend their initiatives in [State] courts. But standing in federal court is a question of federal law, not state law. No matter its reasons, the fact that a State thinks a private party should have standing to seek relief for a generalized grievance cannot override this Court’s settled law to the contrary. Article III’s requirement that a party invoking the jurisdiction of a federal court seek relief for a personal, particularized injury serves vital interests going to the role of the Judiciary in the federal system of separated powers. States cannot alter that role simply by issuing to private parties who otherwise lack standing a ticket to the federal courthouse." ("Hollingsworth v. Perry")
History of legal application
As with all parts of the law, there are exceptions.