Debt buying has historically taken place via the purchase and sale of whole portfolios consisting of a static group of accounts. Debt issuers usually prefer to sell their entire portfolio to a single debt buyer because the issuer is responsible for supplying the debt buyers with the documentation to prove the validity of the account. This documentation known as "media" in the debt buying industry may include the original account application, monthly statements, affidavits of sale and charge-off statements. This information protects consumers and is necessary to prove in court that the debtor owes the money and that the debt buyer owns the account.