Research has improved our understanding of the managerial challenges inherent in exploratory intermediation. For instance knowledge brokers help to solve well-defined problems based on existing competences. But what if the relevant actor networks are not known, if there is no clear common interest, or if there are only ill-defined, wicked problems and no legitimate common place where they can be discussed? The aim of this paper is to explore these management principles for intermediation of the unknown. Can intermediaries be active when the degree of unknown is high? And if so, what can they do and how can they manage and drive collective innovation? We first build on a review of the literature to highlight common core functions of the different types of intermediaries. Then, we introduce the "degree of unknown" as a new dimension for analyzing the role of intermediaries, and we discuss whether the core functions of the intermediary could be fulfilled when the degree of unknown is very high. Our analysis is based on four different empirical case studies in Sweden, France, and Germany where these functions have been tackled in particular because of the low level of pre-existing knowledge. We describe the managerial challenges these intermediaries face in the unknown and we demonstrate examples of how they have been handled. We conclude by discussing the theoretical and empirical perspectives raised by this work. The paper contributes to the theory of innovation intermediaries by exploring the properties of a form of intermediary for which the degree of unknown is a key contingency variable, and describes management principles for such intermediaries. In this way we characterize a new role -the "intermediary of the unknown" - that may be well spread in practice but scarcely analysed in the literature.