Credit card networks are the ones that help process your credit card transactions. When you make a payment to a merchant, they are the ones that route the transactions and confirm that you have credit available to pay for the purchase. Visa, Mastercard, Discover and American Express are networks. Discover and American Express are card issuers as well as networks.Some merchants only accept cards processed by certain networks. If you have a Mastercard, for instance, you won’t be able to use it with a merchant that only accepts American Express cards. In return for the services they provide, networks get paid through credit card transaction processing fees. These fees average 2 to 3 percent of the purchase price, with the majority of this going to the card issuer as a swipe fee. They also include a payment to the merchant's bank and to any payment processor involved in the transaction.