An affidavit ( /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 law. Such statement is witnessed as to the authenticity of the affiant's signature by a taker of oaths, such as a notary public or commissioner of oaths. The name is Medieval Latin for he has declared upon oath. An affidavit is a type of verified statement or showing, or in other words, it contains a verification, meaning it is under oath or penalty of perjury, and this serves as evidence to its veracity and is required for court proceedings.

Affidavits may be written in the first or third person, depending on who drafted the document. If in the first person, the document's component parts are:

If 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.