It has been an enduring misconception that the Smoot-Hawley Tariff Act of 1930 both caused and deepened the Great Depression. Yet a close assessment of the history surrounding the implementation of the law and its impact yields an array of surprising, ironic, and contradictory conclusions that powerfully refute the received wisdom. The tariff revision engineered in the act, coauthored and sponsored by the Republican senator Reed Smoot of Utah and Republican representative Willis Hawley of Oregon, was not, for example, simply the result of specific interest-group pressure in Congress. Its increases in tariff schedules were not, by any historical standards, extreme. In the final analysis, the dramatic collapse of the American economy, which began in October 1929 and continued unrelentingly until March 1933, and the weakness in national product and employment indices that persisted until World War II, cannot be blamed on Smoot-Hawley, which has assumed singular notoriety as an example of disastrous trade policy. These key findings are at the heart of Douglas A. Irwin's focused, pithy, and most welcome book.