What is the importance of the Miranda warning?

Answer

A Miranda Warning is a statement made by police when he is about to question a suspect on a case. Generally it includes that the subject has the right to not answer any questions or stop answering them at any time during the questioning or interrogation, that the subject has the right to have a lawyer present, whether or not he can afford one, and that anything he does say can later be used against him in court should the case get that far.

The Miranda Warning refers to the Supreme Court decision regarding Ernesto Arturo Miranda vs. the State of Arizona,(1966). His conviction was overturned because police didn't inform him of his Constitutional rights when questioned by police.

It should be noted that just because one is read the Miranda Warnings doesn't mean he's under arrest. If you are under arrest the police don't need to question you or read you your rights. Also, there is no obligation for the officer to read the warning out of a card, but this is standard practice to alleviate any doubt in court about the actual content of the warning (whether the officer had forgotten to notify one of the other of the rights)

A Miranda Warning is an official statement that must be read to an individual in police custody before police can begin interrogation. This rule was the result of the US Supreme Court case Miranda v. Arizona, (1966) in which the Supreme Court held Ernesto Arturo Miranda's confession was inadmissible in court because he hadn't been informed of his Fifth Amendment constitutional right not to incriminate himself.

Chief Justice Warren clearly stated the rules governing custodial interrogation in the opinion of the Court:

"In the absence of other effective measures, the following procedures to safeguard the Fifth Amendment privilege must be observed: the person in custody must, prior to interrogation, be clearly informed that he has the right to remain silent, and that anything he says will be used against him in court; he must be clearly informed that he has the right to consult with a lawyer and to have the lawyer with him during interrogation, and that, if he is indigent, a lawyer will be appointed to represent him."

The Court's decision permanently changed law enforcement procedures, such that people taken into police custody must be formally advised of their rights before questioning. Each state is free to determine the exact Wording of their "Miranda Warning," provided the elements stipulated in the Supreme Court decision are clearly included.

Examples

"You have the right to remain silent. Anything you say can and will be used against you in a court of law. You have the right to speak to an attorney, and to have an attorney present during any questioning. If you cannot afford a lawyer, one will be provided for you at government expense."

Some jurisdictions use more elaborate warnings, designed to prevent confessions from being excluded in court:

"You have the right to remain silent and refuse to answer questions. Do you understand?
Anything you do say may be used against you in a court of law. Do you understand?
You have the right to consult an attorney before speaking to the police and to have an attorney present during questioning now or in the future. Do you understand?
If you cannot afford an attorney, one will be appointed for you before any questioning if you wish. Do you understand?
If you decide to answer questions now without an attorney present you will still have the right to stop answering at any time until you talk to an attorney. Do you understand?
Knowing and understanding your rights as I have explained them to you, are you willing to answer my questions without an attorney present?"

Other variations are also used.