An affidavit is a signed, written statement of facts stated to be within the personal knowledge of the person making the statement (the affiant or deponent) that includes a verification—which is a statement that the affiant is swearing to the truth of the statement or making the statement under penalty of perjury—meaning the affiant can be prosecuted for the crime of perjury if they make the statement knowing it is false. An affidavit is also sometimes referred to as a verified statement or a sworn statement.

An affidavit is said to be “made under oath or affirmation.” Traditionally, affidavits were made with a sworn promise or oath before God or a supreme being that the statement was truthful—“the truth, the whole truth, and nothing but the truth, so help me God.” Affidavits are now also made on the alternative basis of an affirmation in which the affiant affirms the truth of the facts under penalty of perjury.

When the affiant signs the statement of facts in the affidavit—after making a spoken oath or affirmation to the notary public (person who administers the oath or affirmation)—the language above the affiant’s signature in which the affiant swears to or affirms the truthfulness of the preceding or foregoing statement is sometimes known as a Verification Upon Oath or Affirmation.

An affidavit must also be notarized—signed by a licensed notary public (notary) and stamped with the notary’s official stamp or seal—which sometimes includes a statement that the named person (affiant) appeared before the notary; the notary confirmed the identity of the affiant; the affiant swore under oath or penalty of perjury (affirmation) that the facts stated in the affidavit are within the affiant’s personal knowledge and are true and correct; and the affiant signed the document in the presence of the notary on the date indicated. This recitation of the making of the affidavit is sometimes called the preamble.

With or without a preamble statement, the notary public must certify that the notary administered an oath or affirmation to the affiant and the affiant signed the affidavit in the presence of the notary. This certification is known a jurat and often includes the words “Sworn to and subscribed before me, the undersigned notary public, by __________(affiant) on this ___ (date) day of ______(month), _______(year).”

Because an affidavit is a sworn statement made under oath or penalty of perjury it is accepted as evidence of the facts stated in many legal contexts, including in some court proceedings.

In Wyoming, an affidavit is a written statement of facts that the affiant (the person making the statement) declares to be true within their personal knowledge, and it is made under oath or affirmation. The affidavit must include a verification, which is the affiant's sworn declaration that the information is true under penalty of perjury. This means that if the affiant knowingly makes a false statement, they can be prosecuted for perjury. Affidavits can be made traditionally with an oath before a deity or on the basis of an affirmation without religious connotations. The affidavit must be notarized, which involves signing the document before a licensed notary public who confirms the identity of the affiant and witnesses the oath or affirmation. The notary's certification, known as a jurat, must state that the affiant signed the document in the notary's presence. Affidavits are commonly used in legal proceedings in Wyoming as evidence of the facts they contain due to their sworn nature.