The Supreme Court decision in Miranda v. Arizona, 384 US 436 (1966) required (for the first time) that someone accused of a crime be informed of his or her constitutional rights prior to interrogation. This protected the rights of the accused, or the defendant, in two new ways: 1) It educated the person about relevant constitutional rights; and 2) It inhibited law enforcement officials from infringing those rights by applying the Exclusionary Rule to any testimony/incriminating statements the defendant made unless he intentionally waived his rights.
The Exclusionary Rule prohibits evidence or testimony obtained illegally or in violation of the constitution from being used against the defendant in court.
The Miranda ruling has been revised somewhat by subsequent Supreme Court decisions. On June 1, 2010, the Roberts' Court released the opinion for Berghuis v. Thompkins, 08-1470 (2010), which held a defendant must invoke his right to remain silent (by stating he wants to remain silent), rather than waiveit (by explicitly agreeing to answer questions before interrogation).
