The first four to six digits of a credit card. The bank identification number identifies the institution issuing the card. It is critical to the correct matching of transactions to the issuer of the charge card.

This prefix system also applies to debit cards, charge cards and electronic benefit cards.

|||Although it is called a bank identification number, BINs are also used by other institutions, such as American Express. As increasing numbers of issuers are opting into the BIN network, the term issuer identification number (IIN) is increasingly used interchangeably with BIN.

The prefix system is also used to help identify potential security breaches or identity theft, by comparing such things as the location of the issuing institution and the address of the cardholder.