In recent years, companies started not only to ask customers by means of market research but to integrate them into the innovation process. Within information systems (IS) research, both customization as a way to serve the uniqueness of customers (inside-out) and as a form of customer integration and value co-creation (outside-in) has been considered. However, since many software vendors have consummated the shift from being manufacturers to being service firms, in practice, customization as a service highlights the continuance of customization projects. This paper addresses the research question of how concepts of customization are distinguished in recent IS literature. By conducting an extensive review of the IS literature between 2001 and 2011 we find that future research could benefit from considering knowledge interactions in customization processes more deeply.