Several types of proximity affect knowledge flows with different strength. Insufficient attention has been paid to the interrelations between such forms of proximity at the same time, each one assumed to facilitate the flow of goods, ideas, and spillovers on its own but not in relation to one another. Moreover, if decreasing returns have been conceptually attributed to proximity effects on the intensity of scientific cooperation and learning processes, empirical evidence about nonlinearities in different proximity effects has never been demonstrated. This article aims to fill these gaps. Results on all Nomenclature of Territorial Units for Statistics (NUTS2) regions of the 27 Countries of the European Union (EU27) point toward the existence and relevance of synergic effects between different types of proximity. In particular, while social proximity has a positive impact on scientific cooperation, with decreasing magnitude as spatial distance increases, results on cognitive and technological proximity suggest that some form of complementarity seems to exist with spatial distance. In fact, when spatial distance increases, in order to cooperate, regions must also be cognitively and technologically close.