The purpose of this paper is to analyse the effect of various proximity dimensions on the innovative capacity of 276 regions in Europe within a knowledge production function model, where R&D and human capital are included as the main internal inputs. We combine the standard geographical proximity with the technological, social and organizational ones to assess whether they are substitutes or complements in channelling knowledge spillovers. Results show that all proximities have a significant complementary role in generating an important flow of knowledge across regions, with technological closeness showing the most important effect.