Abstract
<jats:p>How do production networks and market structure interact to shape the effects of trade and competition policy? We develop a model with two-sided firm heterogeneity, matching frictions, and imperfect supplier competition. More productive buyers match with more suppliers, inducing tougher supplier competition, lower input costs, and higher profits. Entry upstream thus benefits high-productivity buyers, while lower trade or matching costs favor mid-productivity buyers. Empirical evidence confirms that larger French and Chilean firms import higher quantities at lower prices as more Chinese suppliers enter, and that suppliers charge diversified buyers lower markups. We adapt methods for combinatorial, discrete-choice problems to estimate the model and perform counterfactuals. The interaction of endogenous networks and markups significantly amplifies the gains from policies that facilitate supplier entry or firm matching, and from deep trade agreements that combine tariff cuts with such policies. Fixed networks dampen while fixed markups amplify the gains from traditional tariff liberalization.</jats:p>