The presetn work aims at exploring how proximity dimensions can favour the diffusion of knowledge between economic actors, focusing on the knowledge relationships established by a knowledge gatekeeper. In particular, I formulate several hypotheses regarding the role of geographical, organizational, and technologicalproximity dimensions in affecting the establishment of gatekeepers¿ knowledge relationships, taking into account their collaborative-non collaborative type and exploitative-explorative nature. Hypotheses are tested on a sample of 527 knowledge relationships established by two distinct types of knowledge gatekeeper, i.e. a multinational company and a university. In particular, they are the Technical University of Milan and the ST Microelectronics Italy, which represent the Italian university and firm best performing as knowledge gatekeeper.