Business plays a critical yet poorly understood role in trade policymaking. This paper develops an analytical framework that focuses on the distribution of business trade preferences, the forces that cause those preferences to change, and the ability of different groups to exert political influence over policy. It then applies this framework to Mexico in the 1980s and 1990s. Large, exporting firms increased their weight due to shifts in the international context, the condition of the domestic economy, and previous government policies. Policymakers granted political access to actors whose economic and political leverage had risen, typically those who controlled numerous investment resources and sought out a direct role in policymaking. Many of these actors also favored free trade. Business participation in trade policy reflects these patterns. Large, outward-oriented firms played an increasingly important role in Mexico's adoption of free trade policies over the 1980s and early 1990s.