A payment gateway is an online service provider that connects an electronic shopping cart or virtual terminal/POS to an electronic payment processor. It is your gateway to the rest of the payments infrastructure that allows you to accept electronic forms of payment.
The main function of a gateway is to pass authorization, payments, and settlement data securely to and from the merchant's website to the merchant's processor. The merchant processor in turn connects to the card association (or "network"), which connects to the card issuing bank. The articles in this section explain more about the participants in the payments ecosystem, and put gateways in the right context.