Services cannot be produced without customer participation. This aspect involves significant consequences for services management. The integration of the customer and the integration of the external resources that customers need to provide require comprehensive means to coordinate the activities of suppHers and customers. Services management Hterature is based on the idea that the success of service companies mainly depends on an effective and efficient design of supplier and customer interfaces. As a result, academic and practice-oriented service management problems are concerned with managing service processes. However, most approaches are focused on the supplier process side. Here, numerous concepts as well as IT supported tools for service process documentation and service process management have been developed. Customer processes, on the contrary, have mostly been ignored even though it is obvious that they have a high impact on the overall success of the service process. The present work is a major step forward to close that research gap. The author analyses the customer influence on efficiency and effectiveness of the service process depending on the customer's service process knowledge. The empirical data of the thesis was gained from a practice study: it was made in cooperation with a corporate division of T-Systems International that provides business customers with virus wall and firewall service packages for data network security. The study is based on the assumption that service customers have a script, i. e. a relatively precise image of the structure and process of the service transaction.