Apple Pay is a mobile payment service by Apple that allows users to make payments in person, in iOS apps, and on the web. Supported on iPhone, Apple Watch, iPad, Mac, and Vision Pro, Apple Pay digitizes and can replace a credit or debit card chip and PIN transaction at a contactless-capable point-of-sale terminal. It does not require Apple Pay–specific contactless payment terminals; it can work with any merchant that accepts contactless payments. It adds two-factor authentication via Touch ID, Face ID, Optic ID, PIN, or passcode. Devices wirelessly communicate with point of sale systems using near field communication (NFC), with an embedded secure element (eSE) to securely store payment data and perform cryptographic functions, and Apple's Touch ID, Face ID and OpticID for biometric authentication.

Apple Pay can also be used to pay fares on many public transport networks. Payment can be authorised without authentication for supported public transport networks, referred to as 'Express Mode', or by a regular authenticated Apple Pay transaction for other systems accepting contactless payments.

The service is compatible with iPhone 6 and newer, iPad Air 2 and newer, Macs with Touch ID, and Apple Watch Series 1 and later. In iOS 17 or later, the number of cards able to be added to the service is determined by the capacity of the secure element, which varies by device.

Apple Pay uses the EMV Payment Tokenization Specification.

The service keeps customer payment information private from the retailer by replacing the customer's credit or debit card Funding Primary Account Number (FPAN) with a tokenized Device Primary Account Number (DPAN), and creates a "dynamic security code [...] generated for each transaction". The 'dynamic security code' is the cryptogram in an EMV-mode transaction, and the Dynamic Card Verification Value (dCVV) in a magnetic stripe data emulation-mode transaction. Apple added that they would not track usage, which would stay between the customers, the vendors, and the banks. Users can also remotely halt the service on a lost phone via the Find My iPhone service.

To pay at points of sale, users hold their authenticated Apple device to the point of sale system's NFC card reader. iPhone users authenticate by using Touch ID, Face ID, or passcode, whereas Apple Watch users authenticate by double-clicking a button on an unlocked device. To pay in supported iOS apps, users choose Apple Pay as their payment method and authenticate with Touch ID or Face ID. Users can add payment cards to the service in any of four ways: through the payment card listed on their iTunes accounts, by taking a photo of the card, being provisioned from within the card issuer's app, or by entering the card information manually.

Although users receive immediate notification of the transaction, the Apple Pay system is not an instant payment instrument, because the fund transfer between counter-parties is not immediate. The settlement time depends on the payment method chosen by the customer. (An exception being payments made using a card which stores the user's balance on the card itself, such as a Japanese Suica card or a Hong Kong Octopus card. These cards can transfer funds directly to the merchant without the need for an online connection.)

In the United Kingdom, traditional contactless payments using bank cards are limited to £100 (previously £45 until October 14, 2021) as no cardholder authentication is provided as part of the transaction. Payments using Apple Pay, however, support payments of any amount owing to the increased security and lower risk of fraud in Apple Pay transactions (although some issuing banks may impose their own transaction limits, and not all contactless readers support this functionality – see CDCVM below). Similar transaction limits apply in other countries.