Credit Card Verification Number Explained

VISA The Verification Code is a three-digit number on the back of your Visa credit card. The full credit card number is reprinted in the signature box and at the end of the number is the Verification Code.
MasterCard The Verification Code is a three-digit number on the back of your MasterCard. The full credit card number is reprinted in the signature box and at the end of the number is the Verification Code.
Discover The Verification Code is a three-digit number on the back of your Discover card. The full credit card number is reprinted in the signature box and at the end of the number is the Verification Code.
American Express The Verification Code is a four-digit number on the front of the card above the credit card number on either the right or the left side of your American Express credit card.