Perjury statutes in many states make it a crime to knowingly lie after taking an oath to tell the truth, such as when testifying in court or communicating through certain legal documents. The falsehood must usually be material to the matter at issue, though perjury can also be committed by simply signing a document with the knowledge that it contains false assertions.

For example, while completing a sworn affidavit during child support proceedings in family court, Dan purposefully understates his monthly income by $2000, signs the document, and files it with the judge's clerk.