Visa, MasterCard, and Discover
The CVV2 code is 3 digits printed on Visa, MasterCard, and Discover cards in the signature panel on the back of the card. It is the last 3 digits AFTER the credit card number. Sometimes only the last 4 digits of your credit card number will be printed before the CVV2 code instead of the entire credit card number.
 
American Express
The CVV2 code is 4 digits printed on American Express cards above and to the right of the raised credit card number on the front of the card.