Urban economists have long recognized that space is economically important. Evidence of the importance of urban agglomeration and the offsetting effects of congestion are provided in a number of studies of productivity and wages. Little attention has been paid to this evidence in the economic growth literature. The new growth research focuses on technological change. We extend the production function for new ideas common to this research in a way that allows for congestion and agglomeration in innovation and test the hypothesis that these forces are important in explaining innovation. Strong evidence is found that agglomeration and congestion are important in explaining the vast differences in per capita patent rates across US states. This suggests an important new agenda in linking studies of urban economics with the rapidly advancing field of endogenous growth.
