What is the legal term for a voluntary written statement made under oath?

When a court or other legal body needs a formal, written declaration of facts, this is the document they often rely on. It is a voluntary statement of a person's personal knowledge of a situation, written down and signed under oath. The person making the statement, known as the affiant, is essentially swearing that the contents are true to the best of their knowledge, facing the penalty of perjury if they are found to have lied. The term itself comes from the Medieval Latin word meaning "he has declared on oath."

To be legally valid, the document must be signed in the presence of an individual authorized to administer oaths, most commonly a notary public. This official witnesses the signature and adds their own signature and seal, certifying that the affiant was properly sworn in. This process gives the written statement the same legal weight as sworn testimony given in a courtroom.

Affidavits are used in a wide variety of legal situations. They can be used to support motions filed with a court, present evidence in family law cases, confirm the identity of an individual, or state facts during the initial stages of a lawsuit. While it is a form of evidence, it differs from a deposition, which involves live, oral questioning by lawyers. An affidavit is a prepared, one-sided statement used to efficiently present facts in a sworn, written format.