Each major airline gets its own MCC — United is 3000, Lufthansa 3010… That's how 'airline credit card' benefits know what you bought, and how corporate travel policies enforce themselves.
The MCC quietly sets the interchange rate, whether the purchase earns rewards, whether it's treated as a cash advance, and how risk models see the merchant. Acquirers assign it at onboarding — and miscoding is a compliance problem, not a shortcut.
Merchant Category Codes are defined under ISO 18245, with network-specific usage on top. Around 500 exist; the ones that come up in real conversations are in our lookup tool.