Companies face challenges and need support when applying specific knowledge to their innovation processes, such as design for sustainability. The providers of innovation support in innovation systems are intermediaries. While the literature on intermediaries focuses on various roles and approaches, the way in which intermediaries function in specific fields such as design for sustainability remains underexplored. This paper investigates how intermediaries provide innovation support in the design for sustainability field today, with a focus on the services and support they offer, the approaches and drivers that shape them, as well as the challenges of the intermediation process, particularly concerning sustainability and design. To do this, 14 intermediaries from the Netherlands, the United Kingdom and Turkey were investigated through case studies. The role of design in support processes, especially during implementation, the importance and types of collaborations among various actors of innovation systems, and the emergence of a new type of intermediary that promises radical innovation in sustainability are among the findings. In addition, based on the empirical data, we suggest a framework for describing the roles and attributes of a group of five intermediaries that meets the needs of all types of companies engaged in design for sustainability. Finally we offer suggestions for Turkey on how to raise the capacity of its intermediaries operating in the design for sustainability field, which might be applicable to other similar contexts as well. This study contributes to the theory and practice of innovation support in the sustainability field, from which all innovation system's actors, especially intermediaries and governmental institutions, might benefit in designing support programs.