The first 6 digits of your credit card number (including the initial MII digit) form the issuer identifier. This means that the total number of possible issuers is a million (10 raised to the sixth power, or 1,000,000).
Some of the better known issuer identifiers are listed in the following table:
| Issuer | Identifier | Card Number Length |
|---|---|---|
| Diner's Club/Carte Blanche | 300xxx-305xxx, 36xxxx, 38xxxx | 14 |
| American Express | 34xxxx, 37xxxx | 15 |
| VISA | 4xxxxx | 13, 16 |
| MasterCard | 51xxxx-55xxxx | 16 |
| Discover | 6011xx | 16 |
If the MII digit is 9, then the next three digits of the issuer identifier are the 3-digit country codes defined in ISO 3166, and the remaining final two digits of the issuer identifier can be defined by the national standards body of the specified country in whatever way it wishes.