Acquirer
An acquirer—formally known as an acquiring bank—is a licensed financial institution that maintains a direct membership with card networks (such as Visa and Mastercard) to process card transactions on behalf of merchants. Within the card ecosystem, the acquirer acts as the bridge connecting commercial sellers to interbank settlement networks.
Issuer
The issuer—or issuing bank—is the financial institution that provides payment cards, revolving credit lines, and demand deposit accounts to cardholders. As the institution with a direct financial relationship with the consumer, the issuer holds the ultimate authority to approve or decline any transaction presented against its card credentials.
Card networks
Card networks—frequently referred to as card schemes or payment brands (predominantly Visa, Mastercard, American Express, and Discover)—provide the global switching infrastructure, message formats, and legal rulebooks that enable interbank electronic payments.
Processors, gateways, and PSPs
Between a merchant's checkout application and the underlying acquiring bank operates an ecosystem of technology providers and financial intermediaries. Terms like "gateway," "processor," "payment service provider," and "acquirer" are frequently used interchangeably in vendor marketing, obscuring the specific legal and technical roles each company fulfills.
Merchant and cardholder
While acquirers, issuers, and card networks represent institutional infrastructure, merchants and cardholders are the commercial participants at either end of a transaction. Within card scheme rules, the rights and protections granted to each party are fundamentally asymmetric: consumer protections are protected by federal statutes and card scheme rules, whereas the merchant's operational position is governed by its private merchant service contract.
Who is responsible for what
Understanding the technical architecture of payments explains how messages route and how funds clear. However, examining payments through a regulatory and legal lens reveals an entirely different set of operational realities. In financial services, legal obligations do not distribute uniformly across technical vendors; they concentrate heavily upon whichever entity takes custody of consumer funds and whichever institution holds licensed status.