Witnesses in a court proceeding may be convicted of perjury if they intentionally give inaccurate or misleading evidence while they are testifying under oath. Perjury generally occurs in court, but it can also occur when an individual lies on a legal form. Perjury is generally not prosecuted, but if a witness is convicted of perjury they may be required to pay high fines and spend time in jail. Perjury is illegal because it is important that witnesses provide reliable and truthful information in a court case.