Application identifier (AID) is a hexadecimal code stored on an EMV chip that tells a payment terminal which card application to run, such as Visa Debit or Mastercard Credit, and appears on many card receipts. Defined by ISO/IEC 7816-5 and 5 to 16 bytes long, it opens with a 5-byte Registered Application Provider Identifier (RID) naming the scheme. On insertion or tap, the terminal reads the card's AIDs, matches them against its configuration and selects one, whose keys and risk rules govern the rest of the transaction. Under the Durbin Amendment, a US Common Debit AID lets merchants choose a cheaper network. A missing AID makes terminals reject otherwise valid cards.
What is application identifier AID made of
An application identifier (AID) is defined by ISO/IEC 7816-5 and is between 5 and 16 bytes long. The first 5 bytes are the Registered Application Provider Identifier (RID), assigned to a card scheme by an ISO registration authority. The remaining bytes, up to 11, form the Proprietary Application Identifier Extension (PIX), which the scheme uses to distinguish its products.
Common examples:
- A0000000031010: Visa credit or debit.
- A0000000032010: Visa Electron.
- A0000000041010: Mastercard credit or debit.
- A0000000043060: Maestro.
- A0000000980840: Visa US Common Debit.
Visa's RID is A000000003 and Mastercard's is A000000004, so the scheme can be read from the first ten hex characters.
How does AID work in EMV
When a card is inserted or tapped, the terminal asks it which applications it holds. For contact cards it reads the Payment System Environment directory; for contactless payment it reads the Proximity Payment System Environment. The card returns a list of AIDs with labels and priority indicators. The terminal matches them against the AIDs it is configured to accept and selects one, or lets the cardholder choose when more than one is supported and scheme rules allow it.
Once an AID is selected, every later step of the EMV transaction uses that application's keys, risk parameters and cardholder verification rules.
Multiple AIDs on one card
A single card can carry several applications. A European co-badged card may hold both a domestic debit scheme and an international scheme. In the United States, many debit card chips carry a global AID and a US Common Debit AID. Under the Durbin Amendment, issuers must enable at least two unaffiliated networks on each debit card and cannot stop merchants choosing between them, and the common debit AID is what makes that choice possible at the terminal. Selecting it instead of the global AID can lower a merchant's cost on each transaction.
Why AIDs matter to payment businesses
Terminal estates must be configured with the correct AID list for every scheme and product they accept; a missing AID causes the terminal to reject cards that would otherwise work. Acquirers and processors certify their terminals per scheme, and a buyer of an acquiring or POS business will find AID configuration and certification status in the technical due diligence on the terminal estate.