There may be another “face of the coin” for both the customization and the engagement of clients in innovation activities, and KIBS firms may combine different levels of customization and collaboration with clients. This chapter presents the theoretical arguments and empirical evidence provided so far that question the emphasis on client collaboration and KIBS customization, delivers new hypotheses about how KIBS firms should design their service portfolio and client relationships and concludes by introducing the topic of mass customization in KIBS.