Satisfaction has been studied extensively in information systems. Most studies, however, focused on specific system characteristics, providing very little understanding of the process of satisfaction formation. Furthermore, very little is known about the evolution of satisfaction over time, as most previous studies were cross-sectional, implicitly assuming satisfaction to be static. In this research, we address these problems. We develop, operationalize, and empirically test a model that provides a better understanding of customer satisfaction formation in the context of Internet-based services. We also predict/explain the evolution of satisfaction over time from the stage of adoption of Internet-based services to the post-usage stage.