In many jurisdictions other than the United States, witnesses may be compelled under threat of contempt to answer questions even when the answers would incriminate the witness in a criminal offense. (However, in Canada for example, Charter §13 provides automatic use immunity.) In such jurisdictions, such statements given under compulsion of subpoena cannot be used as evidence against that person (which is not the case in the United States). The American system has the benefit of not exposing the witness to the risk that law enforcement will be able to obtain collateral evidence based on the witness's testimony that law enforcement could not possibly have learned had the witness been allowed to remain silent.
A witness may not refuse to answer questions on the ground that the answers may reveal matters that may incriminate other persons. Generally, a witness may not refuse to answer any relevant question put to him or her unless the answer would incriminate that witness. One common application of this rule is the practice of providing limited transactional immunity to a defendant as to specific crimes, thus narrowing the protection against self-incrimination, and permitting a court to compel answers about those crimes. The victim of a crime may be detained and compelled to answer questions, as a material witness, even if the victim does not want to "press charges," on the theory that the crime is of public concern, and the right does not extend to other parties.
As federal grand juries have the power to subpoena individuals and force them to take the witness stand, defendants in such proceedings invariably refuse to answer any questions put to them, citing their Fifth Amendment rights. If the defendant does answer any question put by the prosecutor during the proceeding, the protection of the Fifth Amendment is lost.
One famous example of "taking the fifth" in recent history was when Colonel Oliver North was asked to testify before Congress regarding his role in destroying documents during the Iran-Contra Affair. North refused to answer on the grounds that his answers would incriminate him for obstruction of justice.
The phrase "I take [or plead] the Fifth" is often used in non-legal contexts to convey a reluctance to answer a potentially embarrassing question.