Defence date: 18 June 2014Examining Board: Professor Russell Cooper, Penn State University, Supervisor Professor Arpad Abraham, EUI Professor E.J. Bartelsman, VU University Amsterdam Professor Christian Bayer, University of Bonn.The three chapters of this thesis contribute to a literature which emphasizes the importance of microeconomic heterogeneity for macroeconomic outcomes. In my work I focus on firm heterogeneity. I investigate the US labor market implications of a drop in the number of new firms, study the cyclical effects on productivity due to limits in the reallocation of capital across firms, and quantify the effectiveness of a policy which attempted to save jobs in Germany by altering firm incentives for lay-offs. The first ch...