An affidavit (/ˌaefɨˈdeɪvɨt/ ˌæfɨˈdeɪvɨt-a-Fə-day) vət is a written sworn statement of fact voluntarily made by an affiant or deponent under an oath or affirmation administered by a person authorized to do so by. lawf an affidavit is notarized or authenticated, it will also include a caption with a venue and title in reference to judicial proceedings. In some cases, an introductory clause, called a preamble, is added attesting that the affiant personally appeared before the authenticating authority.