Perjury is the criminal offense of making a false statement under oath—verbally or in writing—that the witness knows to be false and that is material to the proceeding in which the statement is made. And suborning perjury or subornation of perjury is the criminal offense of procuring the perjury of another person.

Perjury is a criminal offense under both state and federal laws and may be prosecuted as a misdemeanor or as a felony offense, depending on the state or federal jurisdiction, and whether there are any aggravating factors that increase the seriousness of the crime. Perjury laws are located in state statutes—often in the penal or criminal code—and the federal perjury law is located in the United States Code at 18 U.S.C. §1621.

In Illinois, perjury is considered a serious criminal offense. Under Illinois law, specifically 720 ILCS 5/32-2, a person commits perjury when, under oath or affirmation, they knowingly make a false statement material to the issue or point in question in any proceeding, whether it be a trial, hearing, or other legal process. Perjury in Illinois is classified as a Class 3 felony, which can result in a prison sentence and fines. Additionally, subornation of perjury, which involves inducing another person to commit perjury, is also a criminal offense under Illinois law and is treated with similar severity. At the federal level, perjury is governed by 18 U.S.C. § 1621, and like Illinois law, it criminalizes the act of willfully making false statements under oath in federal proceedings. The federal statute also allows for the prosecution of individuals who commit perjury, with penalties that can include fines and imprisonment.