Abstract: A customer loyalty card implemented as a smart card (180), including a microchip (200) provided with a processor (304) and a memory (306) as well as a data transfer connection (302) for two-way data transfer with a point-of-sale terminal device. The memory (306) contains a set of card-specific basic information (320), at least one bonus purse (340), an applet (310) provided with a set of functions as well as a programming interface (312) for calling said functions. The functions include reading and writing the bonus purse (340) in response to an input received via the data transfer connection (302). The invention further relates to a point-of-sale terminal system for processing a customer loyalty card, and to a central system for controlling point-of-sale terminal systems.