Issuer Identification Numbers (IIN), also known as bank identification numbers (BIN), are the first six to eight digits of a credit or debit card. Though they may appear to be random series of numbers, they are actually a critical part of the payment industry, as they are used to identify which company issued a card and to validate the card's authenticity.

Each IIN is a unique identifier assigned to a particular credit card issuer and is used by banks and card issuers to distinguish which card provider is authenticating and authorizing a payment transaction. In addition, banks use IINs to check the validity of a credit card before completion of the transaction. For example, before processing a request for a purchase, a bank will access a database to associate the IIN with the logos, brand, and other credentials of the issuing institution and to verify that the card number is authentic.

The four major card providers Visa, Mastercard, American Express, and Discover, all have variations of IINs that correspond to the type of card which is being processed. For example, American Express cards typically begin with the prefix '34' or '37'. Generally, the longer the card number, the higher the risk that the card is fraudulent. Therefore, a longer IIN is used to protect against potential card fraud.

IINs have streamlined the processing of payment transactions in recent years. They allow card companies to quickly validate and authorize card transactions. They also provide greater security for both issuers and consumers by enabling them to verify the validity of a card and determine whether the card issuer is approved.

It is important to note that IIN numbers are just one aspect of card security. Other safety features work in conjunction with IINs to make sure consumers’ cards remain safe. Knowing what an IIN is, however, will help consumers to determine if the card they are using is valid and reduce the chance of fraudulent activity.