This paper estimates the effect of Wal-Mart expansion on retail employment at the county level. Using an instrumental variables approach to correct for both measurement error in entry dates and endogeneity of the timing of entry, I find that Wal-Mart entry increases retail employment by 100 jobs in the year of entry. Half of this gain disappears over the next five years as other retail establishments exit and contract, leaving a long-run statistically significant net gain of 50 jobs. Wholesale employment declines by approximately 20 jobs due to Wal-Mart's vertical integration. No spillover effect is detected in retail sectors in which Wal-Mart does not compete directly, suggesting Wal-Mart does not create agglomeration economies in retail trade at the county level.

Wal-Mart, Toys R Us, and other large retail chains are often identified with cheap imports. We use data from the Census of Retail Trade and the International Trade Commission over the period 1997-2002 to test whether big chains serve as platforms for imports from LDCs. Using difference-in-difference specifications we show that Chinese and other LDC imports have increased disproportionately in retail sectors with the sharpest consolidation into chains. To quantify the importance of chain growth to import growth we apply a numerical algorithm that generates marginal propensities to import by firm size. The largest retail firms' propensity to import from China is 17 percentage points higher than that of smaller retailers; the corresponding difference in import propensities from LDCs as a whole is 27 points. The disproportionate growth of large retailers between 1997 and 2002 explains 5% of the overall growth in consumer goods imports, 20% of the growth in consumer goods imports from China, and 22% of the growth in consumer goods imports from LDCs..

We study the adoption, diffusion, and impacts of the Universal Product Code (UPC) between 1975 and 1992, during the initial years of the bar code system. We find evidence of network effects in the diffusion process. Matched-sample difference-in-differences estimates show that firm size and trademark registrations increase following UPC adoption by manufacturers. Industry-level import penetration also increases with domestic UPC adoption. Our findings suggest that bar codes, scanning, and related technologies helped stimulate variety-enhancing product innovation and encourage the growth of international retail supply chains.