Using US firm level panel data we simultaneously assess the contributions to productivity of three potential sources of research and development spillovers: geographic, technological, and product market ("horizontal"). To do so, we construct new measures of geographic proximity based on the...

We simultaneously assess the contributions to productivity of three sources of research and development spillovers: geographic, technology and product–market proximity. To do this, we construct a new measure of geographic proximity that is based on the distribution of a firm’s inventor...