This article draws from two bodies of literature, innovation intermediaries and technological innovation systems, to develop an approach for analysing the functions of intermediaries in eco-innovation. The link between the functions of innovation intermediaries and the functions of technological innovation systems has seldom been explicitly established in the scientific discourse and thus this article contributes to theoretical development in both literatures. To the technological innovation systems literature, this article addresses the lack of attention to the functions of innovation intermediaries who are a critical part in the formation of networks and also contribute to a number of innovation system functions. To the innovation intermediary literature, the functional approach advocates for a synthesis and consensus building in the literature regarding intermediary functions in view of the several redundancies and ambiguities on the subject matter. Empirical operationalization of the analytical approach including methodological choices from case studies in Region Scania, Sweden and North Rhine Westphalia, Germany are also discussed. The results of our analysis show that the functions of the innovation intermediaries are particularly relevant for the overall goals of an innovation system as compared to the configuration of intermediary actors. Particular challenges with a functional approach in this context include the difficulties of establishing a causal relation between the support functions of intermediaries and eco-innovation outcomes in firms.