Protectionism has been an enduring feature in the world economy even though economic theory can prove that free trade is a superior regime. Protectionism is, of course, caused primarily by interest groups who lose out under free trade and are able to organize to protect their interests. This major reference collection brings together some different theoretical approaches to the issue of commercial policy and how it is constructed. It also illuminates some of the complexities behind alternating phases of comparatively free trade and protectionism in the world economy over the last two centuries. Individual country studies bring out some variety in the experience, both in the origins of protectionist policies and of their impact. The conclusions add up to a considerable indictment of protectionism.