During World War II, the U.S. government launched an unprecedented effort to mobilize science for war: the newly-established Office of Scientific Research and Development (OSRD) entered thousands of R&D contracts with industrial and academic contractors, spending one to two orders of magnitude...

We extend the basic Schumpeterian endogenous growth model by allowing incumbents to undertake innovations to improve their products, while entrants engage in more "radical" innovations to replace incumbents. Our model provides a tractable framework for the analysis of growth driven by both entry...

Using the farm tractor as a case study, I show that lags in technology diffusion arise along two distinct margins, which I term scale and scope. Though tractors are now used in nearly every agricultural field operation and in the production of nearly all crops, they first developed with much...