PT - JOURNAL ARTICLE AU - José Azar AU - Ioana Marinescu AU - Marshall Steinbaum TI - Labor Market Concentration AID - 10.3368/jhr.monopsony.1218-9914R1 DP - 2020 May 12 TA - Journal of Human Resources PG - 1218-9914R1 4099 - http://jhr.uwpress.org/content/early/2020/05/04/jhr.monopsony.1218-9914R1.short 4100 - http://jhr.uwpress.org/content/early/2020/05/04/jhr.monopsony.1218-9914R1.full AB - A product market is concentrated when a few firms dominate the market. Similarly, a labor market is concentrated when a few firms dominate hiring in the market. Using data from the leading employment website CareerBuilder.com, we calculate labor market concentration for over 8,000 geographic-occupational labor markets in the US. Based on the DOJ-FTC horizontal merger guidelines, the average market is highly concentrated. Going from the 25th percentile to the 75th percentile in concentration is associated with a 5% (OLS) to 17% (IV) decline in posted wages, suggesting that concentration increases labor market power.