We develop a tractable dynamic model of productivity growth and technology spillovers that is consistent with the emergence of real world empirical productivity distributions. Firms can improve productivity by engaging in in-house R\&D, or alternatively, by trying to imitate other firms'...

This chapter surveys the costs, risks, and challenges encountered in the progressive discovery and development of new pharmaceuticals. The changing methods by which drugs are discovered, the links between companies and academic science, the changing character of public regulation, and the sharp...