Eco-innovation continues to gain support as a driving force for sustainable development. In this regard, pressing questions include how to stimulate the development, diffusion and use of eco-innovations. Often, firms engaged with eco-innovation need to connect to intermediary organizations (e.g. business development organizations, regional clusters, universities, financers, incubators) to get hold of necessary resources to tackle the challenges in the innovation process. This article analyses the functions of such intermediary organizations for eco-innovation by focusing on public–owned business development organizations and cluster initiatives in the Region Scania, Sweden and North Rhine Westphalia, Germany.  We synthesise at least eight functions of intermediaries for eco-innovation as: (i) forecasting and road mapping (ii) resource mobilization (iii) networking and partnerships (iv) commercialization (v) technical consulting (vi) information scanning and distribution (vii) sector branding and legitimation (viii) prototyping and piloting.  The support functions often take a “one-size-fits-all” approach with few initiatives particularly tailored for eco-innovations. This can be explained by the market complementarity roles of public intermediaries, their resource constraints and the cross-sectoral nature of eco-innovation. Even though, intermediary functions are often appreciated by clients and financers, it is often difficult to establish a causal relation between the support and eco-innovation outcomes, a challenge which undermines the existence of intermediaries themselves. Despite these challenges, potential good practices point to a mix between general “one-size-fits-all” and tailored support activities for different types of eco-innovations and firms. Furthermore, interaction between various types of intermediaries is important since there are often numerous actors and initiatives working with eco-innovation which can confuse firms. When it comes to stimulating radical eco-innovations, a proactive approach to intermediation is particularly important.