This paper gives an overview about customer cards in general and specifically about customer cards in the retail business. As there are many customer card programs, the paper focuses on the M-CUMULUS program of Migros and the Supercard program of Coop. The idea of the paper is to compare these two programs and to show what customer cards are used for. Although the customer can benefit from such programs, it is also the company that profits. As the precondition to benefit of the programs is that the customer always shows his card, the company gets important information and data about the customers. This data is not just used to improved the service for the customer, but to adapt the service offering too.