Immigration to the United States has been a major source of population growth and cultural change throughout much of its history. In absolute numbers, the United States has by far the highest number of immigrants in the world, with 50,661,149 people as of 2019. This represents 19.1% of the 244 million international migrants worldwide, and 14.4% of the United States' population. In 2018, there were almost 90 million immigrants and U.S.-born children of immigrants in the United States, accounting for 28% of the overall U.S. population.

The Immigration and Nationality Act of 1965, also known as the Hart–Celler Act and more recently as the 1965 Immigration Act, is a landmark federal law passed by the 89th United States Congress and signed into law by President Lyndon B. Johnson. The law abolished the National Origins Formula, which had been the basis of U.S. immigration policy since the 1920s. The act formally removed de facto discrimination against Southern and Eastern Europeans as well as Asians, in addition to other non-Western and Northern European ethnicities from the immigration policy of the United States.