The four-party card model has long-been the functional framework for payments, separating issuing and acquiring across key functions
Every card payment involves four distinct parties: the cardholder, the merchant, the issuer, and the acquirer.
Each has a defined role, and the relationship between them determines how a transaction is processed, how funds move, and how costs are distributed.
It’s largely Visa and Mastercard that sit at the centre of this model, not as banks, but as the network infrastructure connecting its moving parts.
The four parties explained
The cardholder: Is the individual making the purchase, using a debit or credit card issued by their bank. The merchant is the business accepting the payment, whether in-store or online.
The issuer: Is the cardholder’s bank or financial institution. It provides the card, holds the funds or extends the credit, and bears the risk if a transaction is fraudulent. When a payment is initiated, the issuer decides whether to approve it.
The acquirer: Is the merchant’s bank. It holds the merchant’s account, processes incoming card transactions on their behalf, and ensures funds are settled.
The card network: Is what sits between the issuer and the acquirer – Visa or Mastercard – whose role is to route communications between the two.
Where Visa and Mastercard fit
Visa and Mastercard are not banks. They do not issue cards, hold deposits, or extend credit. Their function is to operate the network layer, the infrastructure and ruleset that allows issuers and acquirers to communicate reliably across thousands of institutions and markets.
When a cardholder taps a Visa card at a terminal, the acquirer sends an authorisation request through Visa’s network to the issuer. The issuer approves or declines and returns a response through the same route. Visa carries that exchange but holds no financial stake in the transaction itself.
This design allows Visa and Mastercard to operate at global scale without taking on the credit or liquidity risk that comes with actually holding funds.
How funds move
Authorisation happens in real time at the point of sale. When a cardholder initiates a transaction, the merchant’s terminal captures the card data and sends an authorisation request to the acquirer.
The acquirer forwards that request through the card network, Visa or Mastercard, to the issuer. The issuer runs a series of checks: whether the card is valid, whether sufficient funds or credit are available, and whether the transaction triggers any fraud indicators.
It then returns an approval or decline code back through the same chain – network to acquirer to terminal – typically within a few seconds.
Settlement, which is the movement of funds between institutions, follows separately, typically within one to two business days.
At settlement, the merchant does not receive the full transaction value. Several deductions are applied before funds reach the merchant’s account, each corresponding to a different party in the model.
The largest component is the interchange fee, which flows from the acquirer to the issuer. Interchange exists because the issuer carries the majority of the financial risk in the transaction, it has extended credit or guaranteed funds to the cardholder, and it bears the cost if a transaction turns out to be fraudulent or disputed.
The fee is set not by the issuer itself but by the card network, and it varies depending on factors including card type, transaction channel, and merchant category.
A premium rewards credit card, for example, typically attracts a higher interchange rate than a standard debit card, because the issuer needs to fund the rewards programme attached to it.
On top of interchange, the card network, such as Visa or Mastercard, charges its own fee, known as a scheme fee or assessment fee. This is the network’s direct revenue for providing the infrastructure and ruleset that makes the transaction possible.
The acquirer then applies its own margin, which covers the cost of processing, risk management, and its commercial relationship with the merchant.
This is typically negotiated directly between the acquirer and the merchant, and larger merchants are generally able to secure lower rates.
The sum of all three, interchange, scheme fees, and acquirer margin, is what the merchant actually pays to accept a card transaction.
This total is referred to as the merchant discount rate, or MDR. For most merchants, MDR sits somewhere between 0.3% and 2% of the transaction value, though the range is wide and depends heavily on the merchant’s size, sector, and card mix.
Why the model matters
The four-party model has remained the dominant framework for card payments for decades.
By separating issuing and acquiring into distinct functions, it allows competition on both sides of the market independently – banks competing to issue cards to consumers, acquirers competing for merchant business – with a single interoperable network connecting them.
That same structure has attracted significant regulatory attention. Critics argue that Visa and Mastercard, as the central network layer, are positioned to set interchange levels that favour issuers at the expense of merchants. Both networks have faced antitrust proceedings in the US and Europe on this basis.
But, for many working in payments, the four-party model is the foundation point on which payments are authorised, processed, and settled.
