The rise of open innovation practices resulted in an increase of intermediaries for innovation. In this context, the purpose of our paper is to better understand the different reasons why innovative companies use the services of such intermediaries. More specifically, we identify two distinct types of open innovation intermediaries, whose roles are significantly different; while the first type can help companies to reduce transaction costs related to open innovation (e.g. costs related to the identification of partners, drafting contracts, reducing opportunistic behaviors, etc.), the second type may also be implicated directly in the creation, transfer and diffusion of knowledge (especially tacit knowledge). In our paper we illustrate both roles in the case of public research. We clearly distinguish the Technology Transfer Organizations (TTOs), whose role is to reduce the transaction costs related to technology transfer, from Research and Technology Organizations (RTOs) that are actively involved in the knowledge creation and transfer process. JEL Codes: O, O3, O32, O33, O34