A statute of limitations is a statute in a common law legal system setting forth the maximum period of time, after certain events, that legal proceedings based on those events may begin. In civil law systems, these provisions are usually part of the civil code or criminal code and are often known collectively as periods of prescription or prescriptive periods.

A common law legal system might have a statute limiting prosecution for crimes called misdemeanors to two years. In such a state, if a person is discovered to have committed a misdemeanor three years ago, he cannot now be prosecuted for it. Or a contract can only be sued upon for breach or performance from six years after the contract was agreed upon or partially performed.

In contrast, Canada has a criminal limitations periods only for summary summary (less serious) offences. The period is ten years from the date of the offence. Thus, A can only be charged with failing to inform of a hole in ice (an actual offence) within ten years of the time of commission. In the case of indictable (more serious) offences, if A sexually assaulted V, A could be charged any time in the future—even if the crime happened twenty years ago.

A crime (in the case of a criminal prosecution) or a cause of action (in a civil lawsuit) is said to have accrued when the event beginning its time limitation occurs. Sometimes this is the event itself that is the subject of the suit or prosecution (such as a crime or personal injury), but it may also be an event such as the discovery of a condition one wishes to redress, such as discovering a defect in a manufactured good, or in the case of lost memory syndrome where someone discovers memories of childhood sexual abuse during therapy long afterwards.

A special case of the statute of limitations is a statute of repose. This applies to buildings and properties, and limits the time during which an action may lie based upon defects or hazards connected to the construction of the building or premises. An example of this would be that if a person is electrocuted by a wiring defect incorporated into a structure in, say, 1990, a state law may allow him or his heirs to sue only before 1997 in the case of an open (patent) defect, or before 2000 in the case of a hidden defect.

Philosophical justifications

One reason for statutes of limitations is fairness; that is, over time memories fade, evidence is lost or never found, and people prefer to get on with their lives without legal intrusions from the past. The length of these statutes varies from country to country, state to state, or province to province, and often depends on the type of civil action or the seriousness of the crime. Some crimes such as murder are so horrific to society that they have no limitations period in some jurisdictions. Generally causes of action relating to real property have longer limitations periods, slander and libel usually have short periods.

From time to time, controversy arises because some horrific crimes have been discovered, but their perpetrator may finally escape due to the statute of limitation or prescription.

Another reason for statutes of limitations is closure or certainty. At some point, society will no longer make its tribunals available for dispute resolution. Eventually, law enforcement agencies will stop using public resources to investigate a given crime. For civil actions, statutes of limitations usually range between one and ten years. In California, for example, the statute of limitations for most personal injury actions (including those resulting from car accidents) is one year from the date of the accident. In Nevada it is two years, and in New Mexico and New York, three.

When the time expires

Once the statute of limitations on a case runs out, if a party raises it as a defense any further litigation is foreclosed. Most jurisdictions provide that limitations are tolled under certain circumstances. Tolling will prevent the time for filing suit from running while the condition exists. Examples of such circumstances are if the aggrieved party (plaintiff) is a minor, or the defendant has filed a bankruptcy proceeding. In those instances, in most jurisdictions, the running of limitations is tolled until the circumstance (i.e. the injured party reaches majority in the former or the bankruptcy proceeding is concluded in the latter) no longer exists.

There may be a number of factors which will affect the tolling of a statute of limitations. In many cases, the discovery of the harm (as in a medical malpractice claim where the fact or the impact of the doctor's mistake is not immediately apparent) starts the statute running. In some jurisdictions the action is said to have not accrued until the harm is discovered, while in others the action accrues when the malpractice occurs, but an action to redress the harm is tolled until the injured party discovers the harm. An action to redress a tort committed against a minor is generally tolled in most cases until the child reaches the age of majority. A ten-year-old who is injured in a car accident might therefore be able to bring suit one, two or three years after he turns eighteen.

It may also be inequitable to allow a defendant to use the defense of the running of the limitations period, such as the case of an individual in the position of authority over someone else who intimidates the victim into never reporting the wrongdoing, or where one is lead to believe that the other party has agreed to suspend the limitations period during good faith settlement negotiations or due to a fraudulent misrepresentation.

Generally speaking, in the case of private, civil matters the limitations period may be shortened or lengthened by agreement of the parties. While such limitations periods generally are issues of law, limitations periods known as laches may apply in situations of equity, i.e. a judge will not issue an injunction if the party requesting the injunction waited too long to ask for it, such periods are not clearly defined and are subject to broad judicial discretion.