Every credit card has a card verification value, or CVV, consumers may need to provide when making a purchase. American Express refers to the CVV on its cards as a card identification number, or CID. The CID is a four-digit number located just above the card credit number. Unlike the card number, the CID is typically not embossed.
Why It's Important
American Express expects every merchant who accepts its cards to adhere to its CID rules and regulations. These include keying in the CID for in-store purchases and requiring the customer to give it for anything bought online or by phone. The CID is proof you have the card in your possession and are not using a stolen credit card number.
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When You Need It
Unless you're buying in person, you'll need to know the CID. Typically, you don't need the CID when you make in-store purchases because the information is included in the magnetic strip and verified when you swipe. However, according to American Express, some merchants will require the CID as an additional security measure.