UC Davis

National and international flows of knowledge are fundamental determinants of technological progress. In this article we review the existing literature on knowledge flows and we propose a method for estimating them, based on patent citations. Citations are links between inventions that reveal a learning process at the technological frontier. We use data for the period 1975-1996 for 147 subnational regions in Europe and North America. We find that geographical distance and technological differences constitute major barriers to knowledge flows. We also show that these flows may have positive, but small, effect on total factor productivity.