The Fifth Amendment protects witnesses from being forced to incriminate themselves. To "plead the Fifth" or to "take the Fifth" is to refuse to answer a question because the response could form incriminating evidence.
Civil or criminal proceedings
Fifth Amendment protections apply wherever and whenever an individual is compelled to testify. The U.S. Supreme Court has ruled that the privilege against self-incrimination applies whether the witness is in Federal or state court (see Malloy v. Hogan, 378 U.S. 1 (1964)), and whether the proceeding itself is criminal or civil (see McCarthy v. Arndstein, 266 U.S. 34 (1924)).
People have asserted the privilege in grand jury or in congressional hearings in the 1950s, where witnesses testifying before the House Committee on Un-American Activities and the Senate Internal Security Subcommittee claimed the privilege in response to questions concerning their alleged membership in the Communist Party. The amendment has also been used by defendants and witnesses in criminal cases involving the Mafia. The Supreme Court has also used the incorporation doctrine to apply the self-incrimination clause against the states under the Fourteenth Amendment.
The New Jersey Supreme Court recognized the right of a witness to "take the 5th" if called as a witness at a trial. State of New Jersey v. P.Z. (A-21-96) - Decided November 26, 1997
The Supreme Court wrote:
"The Fifth Amendment privilege against self-incrimination, made applicable to the states through the Fourteenth Amendment, provides that “[n]o person . . . shall be compelled in any criminal case to be a witness against himself.” U.S. Const. amend. V. As explained in Malloy v. Hogan, 378 U.S. 1, 8, 84 S. Ct. 1489, 1493, 12 L. Ed.2d 653, 659 (1964), the Fifth Amendment protects “the right of a person to remain silent unless he chooses to speak in the unfettered exercise of his own free will, and to suffer no penalty . . . for such silence.” It reflects our understanding that government is “constitutionally compelled to establish guilt by evidence independently and freely secured, and may not by coercion prove a charge against an accused out of his own mouth.” Ibid.
In New Jersey, the privilege is derived from the common law and is codified in our statutes and rules. State v. Reed, 133 N.J. 237, 250 (1993); see N.J.S.A. 2A:84-19; N.J.R.E. 503. Its importance is not diminished by the lack of specific constitutional articulation; rather, from colonial times, “New Jersey has recognized the right against self-incrimination and has consistently and vigorously protected that right.” Reed, supra, 133 N.J. at 250.
A person invoking the privilege against self-incrimination may do so “'in any . . . proceeding, civil or criminal, formal or informal, where the answers might tend to incriminate him in future criminal proceedings.'” Minnesota v. Murphy, 465 U.S. 420, 426, 104 S. Ct. 1136, 1141, 79 L. Ed.2d 409, 418 (1984) (quoting Lefkowitz v. Turley, 414 U.S. 70, 77, 94 S. Ct. 316, 322, 38 L. Ed.2d 274, 281 (1973)); Banca v. Town of Phillipsburg, 181 N.J. Super. 109, 114-15 (App. Div. 1981); see New Jersey Div. of Youth & Family Servs. v. S.S., 275 N.J. Super. 173, 179 (App. Div. 1994). However, the privilege is not self-executing under either federal or state law and must be invoked by anyone claiming its protection. Murphy, supra, 465 U.S. at 428-29, 104 S. Ct. at 1142-43, 79 L. Ed. 2d at 419-20; Reed, supra, 133 N.J. at 251. Generally, when the privilege is not asserted and the person questioned chooses to answer, the choice to respond is considered voluntary. Murphy, supra, 465 U.S. at 429, 104 S. Ct. at 1143, 79 L. Ed. 2d at 420; State v. Fary, 19 N.J. 431, 435 (1955)."