The numbers found on credit cards and bank cards have a certain amount of internal structure, and share a common numbering scheme. Credit card numbers are a special case of ISO/IEC 7812 bank card numbers.

An ISO/IEC 7812 number contains a single-digit Major Industry Identifier (MII), a six-digit Issuer Identification Number (IIN), an account number, and a single digit check sum calculated using the Luhn algorithm. The MII is considered to be part of the IIN.

The term "Issuer Identification Number" (IIN) replaces the previously used "Bank Identification Number" (BIN). See ISO/IEC 7812 for more information.

The card number's prefix is the sequence of digits at the beginning of the number that determine the credit card network to which the number belongs. The first 6 digits of the credit card number are known as the Issuer Identification Number (IIN). These identify the institution that issued the card to the card holder. The rest of the number is allocated by the issuer. The card number's length is its number of digits.

Cards participating in the IIN system include:

• credit cards
• debit cards
• charge cards
• stored-value cards
• Electronic Benefit Transfer cards

In the United States, IINs are also used in NCPDP pharmacy claims to identify processors, and are printed on all pharmacy insurance cards. IINs are the primary routing mechanism for realtime claims. Each processor has one or more IINs, which it divides into plans by using Group Number and Processor Control Number fields.

Online merchants may use IIN lookups to help validate transactions. For example, if the credit card's IIN indicates a bank in one country, while the customer's billing address is in another, the transaction may call for extra scrutiny.

The prefixes and lengths for the most common card types are:

On November 8, 2004, MasterCard and Diner's Club formed an alliance. Cards issued in Canada and the USA start with 54 or 55 and are treated as MasterCards worldwide. International cards use the 36 prefix and are treated as MasterCards in Canada and the US, but are treated as Diner's Club cards elsewhere. Diner's Club International's website makes no reference to old 38 prefix numbers, and they can be presumed reissued under the 55 or 36 IIN prefix. Effective October 16, 2009, Diner's Club cards beginning with 30, 36, 38 or 39 will be processed by Discover Card. "Discover Network - IIN Range Update" (PDF). Retrieved 2009-01-28.

Effective October 1, 2006, Discover will now be using the entire 65 prefix, not just 650. Also, similar to the MasterCard/Diner's agreement, China Union Pay cards are now treated as Discover cards and accepted on the Discover network.

A search on VISA's website results in many references to card numbers being 16 digits long. However, searching for references to 13-digit cards will turn up no results. All 13-digit account numbers have since been migrated to 16-digit account numbers. At least 2 different schemes were devised for this which included postpending 3 digits to the very end of the account number, and, in more rare cases, inserting 3-digits immediately preceding the (former) final 3-digits (of the old 13-digit number).

Switch was rebranded as Maestro in mid 2007. Maestro is now VISA Electron's main competitor in the European debit card market.

Solo can be used outside of Britain if the card displays Maestro.

The Card Security Code is typically the last three digits printed on the signature strip on the back of the card. In the case of American Express cards, it can be a four-digit number printed (but not embossed) on the front of the card.

• Routing transit number
• International Bank Account Number
• List of Bank Identification Numbers