This paper quantifies the cross-national spillover effects of government and private investment in research and development (R&D), using a panel data set of ten OECD countries. The results show that domestic private research is a significant determinant of both domestic and foreign productivity growth, and that foreign government research stimulates domestic private research. These findings ave significant in that they provide empirical support for arguments in favor of international economic policy coordination, particularly in the area of international science and technology.