Suppose firms are subject to decreasing returns and permanent idiosyncratic productivity shocks. Suppose also firms can only stay in business by continuously paying a fixed cost. New firms can enter. Firms with a history of relatively good productivity shocks tend to survive and others are forced to exit. This paper identifies assumptions about entry that guarantee a stationary firm size distribution and lead to balanced growth. The range of technology diffusion mechanisms that can be considered is greatly expanded relative to previous work. High entry costs slow down the selection process and imply slow aggregate growth. They also push the firm size distribution in the direction of Zipf’s law.

In high-tech industries, one important method of diffusion is through employee mobility: many of the entering firms are started by employees from incumbent firms using some of their former employers’ technological know-how. This paper explores the effect of incorporating this mechanism in a general industry framework by allowing employees to imitate their employers’ know-how. The equilibrium is Pareto optimal since the employees “pay” for the possibility of learning their employers’ know-how. The model’s implications are consistent with data from the rigid disk drive industry. These implications concern the effects of know-how on firm formation and survival.