Increasingly heterogeneous customer demands in software development have led to growing research into the effectiveness of customization projects. Despite the widespread assumption of a positive relationship between customer involvement and project success, there is limited empirical research on the mechanism that translates customer knowledge into project success and other positive customer outcomes. This research explores how customer-enabled market knowledge, clarity of requirements and frequency of requirements changes affect the success of software customization projects as well as customer satisfaction and loyalty. The authors employ a multimethod case study design that consists of qualitative and quantitative elements. The results indicate that customer knowledge differently affects the clarity of requirements and the frequency of requirements change. In addition, the authors found support for a positive association between the clarity of requirements and customer loyalty. The authors end with delineating the next steps of this research and possible general future research directions.