Card security codes can have different names -- Card Security Code (CSC), Card Verification Value (CVV or CV2 or CVV2), Card Identification Number (CID), or Card Code Verification (CCV). Regardless of what you call them, the three or four digits provide an additional measure of credit card security when you make purchases online or by mail order, but finding them can be confusing.
VISA/MasterCard/Discover:
The Card Security Code is a 3-digit number located on the BACK of the credit card. In the signature box or just to the right of it, you will see a series of digits. However long the series, the final three digits are the security code.
MasterCard and VISA call this the CVV2 number:
Discover refers to the security code as the CID:
American Express:
On American Express cards, the Card Security Code is a 4-digit number printed on the FRONT of the card, above the card number on the far right side.
If you can't read the security code:
If you can't read the security code for any reason, call the card issuer's customer service number listed on the back of your credit card. Each financial institution has its own guidelines for how to handle illegible security codes, and it may require reissuing the card.