Miranda v. Arizona, 384 U.S. 436 (1966), was a landmark decision of the United States Supreme Court which passed 5-4. The Court held that both inculpatory and exculpatory statements made in response to interrogation by a defendant in police custody will be admissible at trial only if the prosecution can show that the defendant was informed of the right to consult with an attorney before and during questioning and of the right against self-incrimination prior to questioning by police, and that the defendant not only understood these rights, but voluntarily waived them. This had a significant impact on law enforcement in the United States, by making what became known as the Miranda rights part of routine police procedure to ensure that suspects were informed of their rights. The Supreme Court decided Miranda with three other consolidated cases: Westover v. United States, Vignera v. New York, and California v. Stewart.
The Miranda warning (often abbreviated to "Miranda," or "Mirandizing" a suspect) is the name of the formal warning that is required to be given by police in the United States to criminal suspects in police custody (or in a custodial situation) before they are interrogated, in accordance with the Miranda ruling. Its purpose is to ensure the accused is aware of, and reminded of, these rights under the U.S. Constitution, and that they know they can invoke them at any time during the interview.
As of the U.S. Supreme Court decision Berghuis v. Thompkins (June 1, 2010), criminal suspects who are aware of their right to silence and to an attorney, but choose not to "unambiguously" invoke them, may find any subsequent voluntary statements treated as an implied waiver of their rights, and which may be used in evidence.