This paper investigates the causes of the shortfall in private R&D expenditure of the EU compared to the US. It shows that differences in the structure of the two economies play only a minor role in explaining the R&D gap. Instead, the European R&D shortfall is mainly caused by a negative intrinsic effect, meaning that companies within European industries spend less on R&D than their US peers in the same sectors. In addition, this negative intrinsic effect is mainly due to institutional differences between the US and the EU15. Government funding of R&D and the internationalization of R&D provide significant explanation as well.