Injunctionin law, a writ (order) of a court requiring a party to refrain from doing something he proposes to do or to stop doing what he has already started. Cases arise at law in which the ordinary legal procedure, if followed, might cause a great injury to one of the parties. For example, if Brown is about to turn aside a stream that provides water for Smith's cattle, Smith may obtain an injunction to stop the action. If Smith had to wait and bring suit for damages, his cattle might be dead before the case could be tried. The judge hears and decides the injunction case without a jury. If Brown violates the order he may be punished by the judge for contempt of court.

Formerly, injunctions were issued by chancery courts in England and by courts of equity in the United States. Now a few states still have separate courts of law and equity but in most states the same courts administer both law and equity.

There are three kinds of injunctions. In the Brown-Smith example, the judge might issue a temporary restraining order on the application of Smith without giving notice to Brown. Then, after giving Brown a chance to present his case, the judge might either withdraw the order or issue a temporary injunction. Finally, after a full hearing attended by both Brown and Smith, the judge might either withdraw the order or issue a permanent injunction.

In the United States employers formerly obtained injunctions to curb strikes. Labor carried on a bitter campaign against this use of the writ. The Norris-LaGuardia Anti-Injunction Act of 1932 greatly restricted the use of federal court injunctions in labor disputes. Under the Taft-Hartley Act of 1947, however, the President may seek an injunction delaying for 80 days any strike that threatens the national health and safety.