This thesis has described research activities aimed to investigate how e-commerce EPSs could be designed from the user-centered perspective in order to achieve user acceptance. The research has explored what validated design knowledge that should be communicated to designers of EPSs, so that end users will be willing to use the newly introduced EPSs for payments and personal finance in an e-commerce environment. This research aimed to understand the notion of user acceptance in the context of e-commerce EPSs, which is defined as the demonstrable willingness of users to employ information technology for the tasks it is designed to support, (Dillon & Morris, 1996). This research has taken into account various factors that determine user acceptance of electronic payment systems, such as usability, privacy, security, trust and others, (Chapter 2). A combination of various scientific and design activities, and practices of Human-Computer Interaction were involved: a literature study, a consumer survey, a qualitative diary study, and experimental research. These research activities helped to develop an in-depth view of user experience with payment systems and have suggested how to design or redesign EPSs to improve their chances of acceptance by end users.