R&D investment is an important driver of productivity gains. However, firms differ in their ability to appropiate the returns to their R&D efforts. This paper analyses to what extent firm's internationalization influences the endogenous relation between R&D and productivity. In particular, we assess the contribution of R&D to productivity for a panel of UK firms that differ in their degree of internationalization. We find that, on average, multinationals obtain higher gains from their investment in R&D. However, the influence of internationalization on the contribution of R&D to productivity varies along the distribution of the returns to R&D. Keywords: R&D, Multinationals, Productivity. JEL Codes: C14, D24, F23.