Innovating firms can choose to engage in either internal or external R&D, or in both. In the current study, we shall examine internal and external R&D separately to determine empirically the market structure characteristics explaining the external R&D share and the differences in market structure determinants between internal and external R&D. Our results indicate that a government policy that aims at stimulating technological progress by offering external research facilities is particularly interesting for smaller, capital-intensive firms operating in less concentrated markets.