The World Trade Organization (WTO) oversees the negotiation and enforcement of formal rules governing international trade. Why do countries choose to adjudicate their trade disputes in the WTO rather than settling their differences on their own? This book investigates the domestic politics behind the filing of WTO complaints and reveals why formal dispute settlement creates better outcomes for governments and their citizens. It demonstrates that industry lobbying, legislative demands, and international politics influence which countries and cases appear before the WTO. Democratic checks and balances bias the trade policy process toward public lawsuits and away from informal settlements. Trade officials use legal complaints to manage domestic politics and defend trade interests. WTO dispute settlement enables states and domestic groups to signal resolve more effectively, thereby enhancing the information available to policymakers and reducing the risk of a trade war. The book establishes this argument with data on trade disputes and landmark cases, including the Boeing-Airbus controversy over aircraft subsidies, disagreement over Chinese intellectual property rights, and Japan's repeated challenges of U.S. steel industry protection. The book explains why the United States gains better outcomes for cases taken to formal dispute settlement than for those negotiated. Case studies of Peru and Vietnam show that legal action can also benefit developing countries.