The three essays in this dissertation examine how differences across firms shape macroeconomic outcomes. These essays combine models of heterogeneous firms with detailed micro data to answer long-running questions about the U.S. economy: how well are resources allocated across firms? Does globalization drive income inequality? How large are the economic spillovers of firm reputation? Each essay highlights a different aspect of firm or industry heterogeneity that meaningfully changes the answer to the question at hand. Chapter 1, from a work with Sui-Jade Ho, quantifies misallocation in the U.S. manufacturing sector using a structural model and restricted microdata from the U.S. Census. The estimated misallocation---the distance between agg...