This paper exploits product-level U.S. Import data to test trade theory. Although the United States increasingly sources the same products from both high- and low-wage countries, unit values within products vary systematically with exporter relative factor endowments and exporter production techniques.These facts reject factor-proportions specialization across products but are consistent with such specialization within products. The data are inconsistent with new trade theory models predicting an inverse relationship between price and producer productivity. The existence of within-product specialization is an important consideration for understanding the impact of globalization on firms and workers, the evolution of total factor productivity, and the likelihood of long-run income convergence.