The Revenue Act of 1913, also known as the Underwood Tariff or the Underwood-Simmons Act, re-established a federal income tax in the United States and substantially lowered tariff rates. The act was sponsored by Representative Oscar Underwood, passed by the 63rd United States Congress, and signed into law by President Woodrow Wilson.

Tariffs have historically served a key role in the trade policy of the United States. Their purpose was to generate revenue for the federal government and to allow for import substitution industrialization by acting as a protective barrier around infant industries. They also aimed to reduce the trade deficit and the pressure of foreign competition. Tariffs were one of the pillars of the American System that allowed the rapid development and industrialization of the United States. The United States pursued a protectionist policy from the beginning of the 19th century until the middle of the 20th century. Between 1861 and 1933, they had one of the highest average tariff rates on manufactured imports in the world. However American agricultural and industrial goods were cheaper than rival products and the tariff had an impact primarily on wool products. After 1942 the U.S. began to promote worldwide free trade, but after the 2016 presidential election has gone back to protectionism.