An affidavit is a document in which you make statements verified by your oath or affirmation that the statements are true. An affidavit is usually required when someone wants you to make specific statements in writing under the penalty of perjury. There are some types of affidavits that are requested frequently by financial institutions and government departments. Others may need to be tailored to your specific situation. If it is common practice for the financial institution or government department to request a particular affidavit, they may already have a prepared form that they can provide to you. Then you would simply need to fill it out and then swear an oath or affirmation with respect to its contents in front of a notary public or a commissioner of oaths who has the authority to administer oaths.