Perjury is the act of lying or making verifiably false statements on a material matter under oath or affirmation in a court of law or in any of various sworn statements in writing. Perjury is a crime because the witness has sworn to tell the truth and, for the credibility of the court, witness testimony must be relied on as being truthful. The rules for perjury apply when a person has made a statement under penalty of perjury, even if the person has not been sworn or affirmed as a witness before an appropriate official. Perjury is the act of lying or making verifiably false statements on a material matter under oath or affirmation in a court of law or in any of various sworn statements in writing. Perjury is a crime because the witness has sworn to tell the truth and, for the credibility of the court, witness testimony must be relied on as being truthful. The rules for perjury apply when a person has made a statement under penalty of perjury, even if the person has not been sworn or affirmed as a witness before an appropriate official.