American Express and Discover: Network and issuer
Unlike Visa and Mastercard, American Express and Discover are both networks and issuers. This means that even if your American Express or Discover card is branded with a bank or company, your card will likely comes directly from them.
As issuers and networks, American Express and Discover set the fees for both the cardholder and the merchants who make sales through their network.
Unlike Visa and Mastercard, American Express and Discover handle their own customer service. If you lose your Amex in France, you’ll contact American Express directly, whereas you’ll have to call your issuing bank if you lose your Visa.