The Immigration Act of 1924, or Johnson–Reed Act, including the National Origins Act, and Asian Exclusion Act (Pub.L. 68-139, 43 Stat. 153, enacted May 26, 1924), was a United States federal law that limited the annual number of immigrants who could be admitted from any country to 2% of the number of people from that country who were already living in the United States in 1890, down from the 3% cap set by the Immigration Restriction Act of 1921, according to the Census of 1890. It superseded the 1921 Emergency Quota Act. The law was aimed at further restricting the Southern and Eastern Europeans, among them Jews who had migrated in large numbers since the 1890s to escape persecution in Poland and Russia, as well as prohibiting the immigration of Middle Easterners, East Asians, and Indians. According to the U.S. Department of State Office of the Historian the purpose of the act was "to preserve the ideal of American homogeneity". Congressional opposition was minimal.
The Immigration Act made permanent the basic limitations on immigration into the United States established in 1921 and modified the National Origins Formula established then. In conjunction with the Immigration Act of 1917, it governed American immigration policy until the passage of the Immigration and Nationality Act of 1952, which revised it completely.
For the next three years, until June 30, 1927, the 1924 Act set the annual quota of any nationality at 2% of the number of foreign-born persons of such nationality resident in the United States in 1890. That revised formula reduced total immigration from 357,803 in 1923–24 to 164,667 in 1924–25. The law's impact varied widely by country. Immigration from Great Britain and Ireland fell 19%, while immigration from Italy fell more than 90%.