perjury, in law, the giving of false testimony under oath on an issue or point of inquiry regarded as material.
Both traditional and modern legal systems have provisions for taking testimony under oath and mandate penalties for giving false testimony. Islamic law, for example, relies heavily on testimony under oath for criminal convictions. The teachings of Muhammad as recorded in the Qurʾān contain clear injunctions against making a false oath and specify penalties when it occurs.
Perjury originally consisted of the giving of false evidence on oath to a court of law, but in the 19th century its definition was expanded to include the giving of false evidence under affirmation to other tribunals that have the authority of the law. Perjury may be committed by witnesses from either the prosecution or the defense (or by witnesses on either side in civil litigation) and in proceedings before the jury or after the verdict in proceedings leading to sentence.
To be guilty of perjury, an accused person must exhibit criminal intent—i.e., the person must make a false statement and must either know the statement to be false or not believe it to be true. In addition, the false statement must be material to the matters at issue in the proceedings; a person normally may not be charged with perjury if the prosecutor has elicited the false testimony solely to obtain evidence for the charge of perjury. A person who makes a false statement but later corrects it has not committed perjury. In many jurisdictions the law imposes special requirements for the proof of perjury; one such requirement is that a person cannot be convicted of perjury on the testimony of only one witness.
The giving of false testimony under oath distinguishes perjury from criminal contempt, which is an obstruction of the administration of justice, usually in violation of an order of the court. Some perjuries that have the effect of obstructing the adjudication of a case may be given increased punishment for that reason. Generally, however, punishment is directed less against the effect of the perjury than against the disregard of the oath itself. Thus, a person who commits perjury numerous times during the adjudication of a case may be convicted of only a single perjury, though the punishment may be increased.
Crimes associated with perjury include subornation of perjury (persuading other persons to commit perjury or knowing of another’s perjury and failing to make that information known to authorities) and a wide variety of statutory offenses involving making false statements in official documents (such as an application for a driver’s license).