Firms, Destinations, and Aggregate Fluctuations, joint with Julian di Giovanni and Isabelle Mejean Abstract: This paper uses a database covering the universe of French manufacturing firms for the period 1990--2007 to provide a forensic account of the role of individual firms in generating aggregate fluctuations. We first decompose aggregate sales growth into its intensive and extensive components. The extensive margin of entering and exiting firms accounts for about 25% of the growth rate of total output in an average year, but the year-to-year variation in output growth is accounted for primarily by movements in the intensive margin. We next set up a simple multi-sector model of heterogeneous firms selling to multiple markets to motivate a theoretically-founded set of estimating equations that decompose firms' annual sales growth rate into different components. We find that the idiosyncratic firm components contribute substantially to aggregate volatility, mattering about as much as the country-level and sectoral components. The finding that idiosyncratic firm-level shocks appreciably affect aggregate volatility is evidence for the importance of large firms for aggregate fluctuations. JEL Classification Codes: F12, F15, F41 Keywords: Macroeconomic Volatility, Firm-Level Idiosyncratic Shocks, Large Firms, International Trade