Most of the empirical studies assessing the R&D-productivity relationship at the country level fail to consider the possible simultaneity of these variables. Using a 65-country panel for the period between 1965 and 2005, this paper studies the relationship between R&D and productivity using several R&D indicators. We establish that per capita R&D expenditure is strongly exogenous to productivity. This result allows us to develop a further argument that demonstrates the high social returns to R&D spending. Our estimates also indicate that a 10% increase in R&D per capita generates an average increase of about 1.6% in the long-run TFP.