#Major Industry Identifier (MII) # #The first digit of a credit card number is the Major Industry Identifier (MII), which represents the category of entity which issued the card. MII digits represent the following issuer categories: #0 – ISO/TC 68 and other future industry assignments #1 – Airlines #2 – Airlines and other future industry assignments #3 – Travel and entertainment and banking/financial #4 – Banking and financial #5 – Banking and financial #6 – Merchandising and banking/financial #7 – Petroleum and other future industry assignments #8 – Healthcare, telecommunications and other future industry assignments #9 – National assignment #For example, American Express, Diner's Club, Carte Blanche, and JCB are in the travel and entertainment category; VISA, MasterCard, and Discover are in the banking and financial category (Discover being in the Merchandising and banking/financial category); and Sun Oil and Exxon are in the petroleum category. module CreditCardValidations module Mmi ISSUER_CATEGORIES = { '0' => 'ISO/TC 68 nd other industry assignments', '1' => 'Airlines', '2' => 'Airlines and other industry assignments', '3' => 'Travel and entertainment and banking/financial', '4' => 'Banking and financial', '5' => 'Banking and financial', '6' => 'Merchandising and banking/financial', '7' => 'Petroleum and other industry assignments', '8' => 'Healthcare, telecommunications and other industry assignments', '9' => 'National assignment' } def issuer_category ISSUER_CATEGORIES[@number.to_s[0]] end end end