An important subtext across the chapters has been that it is not always, even in principle, possible to identify and attract the “right” participants or even a “right mix” of participants. The differences among the people seen relevant for design may call for different arrangements, and shoehorning all the potential participants and reasons for design participation into any single “format” or method will do injustice to some participants as well as miss opportunities with others. Meaningful participation in different contexts, for different issues, and with different people is a practical (and often anxious) achievement across several competing “goods.” One avenue toward resolving this quandary is the concept of a “participation mix” in which different but related formats complement each other. Participation mixes can be built to offer complementary ways of design participation to enable meaningful participation across the differences present among potential participants; differences in the preferred ways of participating that these people hold; diversity in the design and knowledge needs present in the design project(s); differences in potential participants’ design ability and willingness to engage in design; and often also (the finite) resources available for organizing participation. The idea of a participation mix is not new per se, yet it has remained less elaborated than it should be. Medium and large participatory and human-centered design projects have always conducted complementary user research and user-involvement activities either in sequence or in parallel to address different users and knowledge and the design needs of the projects. Just as well, large private companies have hosted user groups to similar effects, segmenting them according to voluntary participants’ abilities and interests in, for example, segments involved in future trend scanning, concept development, usability and user experience testing, end-user innovation, and prioritization of development requests. What has remained missing has been reflections of the rationales for building up the mix; thus, we take steps toward that by examining the participation mix we developed for the Oodi Central Library in Helsinki. In the latter part of this chapter, we discuss how the resulting complexity of how different participations and ways of knowing the citizen/user/customer insights relate to organizations and institutions has been treated superfluously. To remedy this, the chapter elaborates on “ecologies of user knowledge” mapping tools that help a more analytical approach to starting points for and long-term achievements resulting from design participation. The chapter consequently elaborates the import of ecologies of user knowledge with two cases at the Finnish National Broadcasting Company.