An affidavit is a sworn statement that can be used as evidence in a case, on a motion or at trial. The process of completing an affidavit involves writing out the facts that you are attesting to and swearing the contents to be true in front of a Commissioner of Oaths (e.g. a lawyer). While most people think of oral testimony when they think of evidence, there is a wide variety of circumstances where an affidavit can be entered as evidence without calling the person who swore it to testify.