In American law, a matter is moot if further legal proceedings with regard to it can have no effect, or events have placed it beyond the reach of the law. Thereby the matter has been deprived of practical significance or rendered purely academic.
This is different from the ordinary British meaning of "moot", which means "debatable". The shift in usage was first observed in the United States. The U.S. development of this word stems from the practice of moot courts, in which hypothetical or fictional cases were argued as a part of legal education. These purely academic issues led the U.S. courts to describe cases where developing circumstances made any judgment ineffective as "moot". The doctrine can be compared to the ripeness doctrine, another judge-made rule, that holds that judges should not rule on cases based entirely on anticipated disputes or hypothetical facts. Similar doctrines prevent the federal courts of the United States from issuing advisory opinions.
U.S. Federal Courts 
In the U.S. federal judicial system, a moot case must be dismissed, there being a constitutional limitation on the jurisdiction of the federal courts. The reason for this is that Article Three of the United States Constitution limits the jurisdiction of all federal courts to "cases and controversies". Thus, a civil action or appeal in which the court's decision will not affect the rights of the parties is ordinarily beyond the power of the court to decide, provided it does not fall within one of the recognized exceptions.
A textbook example of such a case is the United States Supreme Court case DeFunis v. Odegaard, 416 U.S. 312 (1974). The plaintiff was a student who had been denied admission to law school, and had then been provisionally admitted during the pendency of the case. Because the student was slated to graduate within a few months at the time the decision was rendered, and there was no action the law school could take to prevent that, the Court determined that a decision on its part would have no effect on the student's rights. Therefore, the case was dismissed as moot.
However, there is disagreement as to both the source of the standards, and their application in the courts. Some courts and observers opine that cases must be dismissed because this is a constitutional bar, and there is no "case or controversy"; others have rejected the pure constitutional approach and adopted a so-called "prudential" view, where dismissal may depend upon a host of factors, whether the particular person has lost a viable interest in the case, or whether the issue itself survives outside the interests of the particular person, whether the circumstance are likely to recur, etc. In actual practice, the U.S. federal courts have been uneven in their decisions, which has led to the accusation that determinations are ad hoc and 'result-oriented.'
There are three major exceptions to this mootness rule. These are cases of "voluntary cessation" on the part of the defendant; questions that are "capable of repetition, yet evading review"; and questions involving class actions where the named party ceases to represent the class.
Voluntary cessation 
Where a defendant is acting wrongfully, but ceases to engage in such conduct once a litigation has been threatened or commenced, the court will still not deem this correction to moot the case. Obviously, a party could stop acting improperly just long enough for the case to be dismissed and then resume the improper conduct. For example, in Friends of the Earth, Inc. v. Laidlaw Environmental Services, Inc., 528 U.S. 167 (2000), the Supreme Court held that an industrial polluter, against whom various deterrent civil penalties were being pursued, could not claim that the case was moot, even though the polluter had ceased polluting and had closed the factory responsible for the pollution. The court noted that so long as the polluter still retained its license to operate such a factory, it could open similar operations elsewhere if not deterred by the penalties sought.
Capable of repetition, yet evading review 
A court will allow a case to go forward if it is the type for which persons will frequently be faced with a particular situation, but will likely cease to be in a position where the court can provide a remedy for them in the time that it takes for the justice system to address their situation. The most frequently cited example is the 1973 United States Supreme Court case of Roe v. Wade, 410 U.S. 113 (1973), which challenged a Texas law forbidding abortion in most circumstances. The state argued that the case was moot because plaintiff Roe had given birth and was no longer pregnant by the time the case was heard. As Justice Blackmun wrote in the majority opinion:
The normal 266-day human gestation period is so short that the pregnancy will come to term before the usual appellate process is complete. If that termination makes a case moot, pregnancy litigation seldom will survive much beyond the trial stage, and appellate review will be effectively denied. Our law should not be that rigid.
Norma McCorvey, whose alias was Roe, became a pro-life advocate and attempted to have the decision of Roe v. Wade reversed and in 'McCorvey v. Hill, 2004, the case failed to proceed based on being moot, without standing and out of time.
The Court cited Southern Pacific Terminal Co. v. ICC, 219 U.S. 498 (1911), which had held that a case was not moot when it presented an issue that was "capable of repetition, yet evading review". Perhaps in response to increasing workloads at all levels of the judiciary, the recent trend in the Supreme Court and other U.S. courts has been to construe this exception rather narrowly.
Many cases fall under the "capable of repetition" doctrine; however, because there is a review process available under most circumstances, the exception to declaring mootness did not apply to such cases. In Memphis Light, Gas & Water Div. v. Craft, 436 U. S. 1, 8–9 (1978), the court noted that claims for damages save cases from mootness.
Class action representatives 
Where a class action lawsuit is brought, with one named plaintiff actually representing the interests of many others, the case will not become moot even if the named plaintiff ceases to belong to the class that is seeking a remedy. In Sosna v. Iowa, 419 U.S. 393 (1975), the plaintiff represented a class that was challenging an Iowa law that required persons to reside there for a year before seeking a divorce in Iowa's courts. The Supreme Court held that, although the plaintiff successfully divorced in another state, her attorneys could continue to competently advance the interests of other members of the class.
U.S. State Courts 
The U.S. state courts are not subject to the Article III limitations on their jurisdiction, and some state courts are permitted by their local constitutions and laws to render opinions in moot cases where the establishment of a legal precedent is desirable. They may also establish exceptions to the doctrine. For instance, in some state courts the prosecution can lodge an appeal after a defendant is acquitted: although the appellate court cannot set aside a not-guilty verdict due to double jeopardy, it can issue a ruling as to whether a trial court's ruling on a particular issue during the trial was erroneous. This opinion will then be binding on future cases heard by the courts of that state.
Some U.S. states also accept certified questions from the federal courts or the courts of other states. Under these procedures, state courts can issue opinions, usually for the purpose of clarifying or updating state law, in cases not actually pending in those courts.
Outside of the U.S. 
Although free from the U.S. Constitutional limitation, Canada has recognized that considerations of judicial economy and comity with the legislative and executive branch may justify a decision to dismiss an allegedly moot case, as deciding hypothetical controversies is tantamount to legislating. Considerations of the effectiveness of advocacy involved in the adversarial system and the possibility of recurrence of an alleged constitutional violation may sway the court. Additionally, the federal and provincial governments can ask for advisory opinions in hypothetical scenarios, termed reference questions, from their respective highest courts.
See also 
|Look up moot in Wiktionary, the free dictionary.|
- Mock trial – A simulated trial (typically of fact)
- Hall, Mathew I (August 2008). "The Partially Prudential Doctrine of Mootness". George Washington Law Review (University of the Pacific, McGeorge School of Law) 77: 562. Retrieved August 14, 2012.
- See, Lochner, Todd, Court Budgets and the Mootness Doctrine The Justice System Journal, pp. 225-226.
- Hall, supra.
- Statute of limitations
- "Slip: Alvarez v. Smith (2009)".
- Prejudice Pushes Aside Mootness Doctrine Hamilton v. Lethem (HSC October 14, 2008).
- See, e.g., Indiana Rules of Appellate Procedure, Title XI, Rule 64, "Certified Questions of State Law From Federal Courts".
- Morton, Frederick Lee, (March 2002) Law, politics, and the judicial process in Canada (BPR Publishers) 660pp. ISBN 978-1-55238-046-8.