The goal of this paper is twofold. First, we aim to assess the role played by inventors' cross-regional mobility and collaborations in fostering knowledge diffusion across regions and subsequent innovation. Second, we intend to evaluate the feasibility of using mobility and co-patenting information to build cross-regional interaction matrices to be used within the spatial econometrics toolbox. To do so, we depart from a knowledge production function where regional innovation intensity is a function not only of the own regional innovation inputs but also external accessible knowledge stocks gained through interregional interactions. Differently from much of the previous literature, cross-section gravity models of mobility and co-patents are estimated to use the fitted values to build our “spatial” weights matrices, which characterize the intensity of knowledge interactions across a panel of 269 regions covering most European countries over 6 years.