This short book has a novel thesis, which is that the degree of factor mobility at the national level influenced the politics of foreign-trade policies. When factor mobility was high, tariff legislation was class legislation. When mobility was low, tariffs were decided by interest-group competition. Michael Hiscox brings data on mobility to bear on the history of foreign trade policies of the six countries—the United States, Britain, France, Sweden, Canada, and Australia—over the last one or two hundred years or so, devoting a chapter to each. He then tests his ideas quantitatively on U.S. congressional voting between 1924 and 1994, finding that, when the indicators of factor mobility were low, an “interest group theory” better explains U.S. tariff politics than does a “class legislation theory” (and the reverse when mobility was high).