A melting pot is a monocultural metaphor for a heterogeneous society becoming more homogeneous, the different elements "melting together" with a common culture; an alternative being a homogeneous society becoming more heterogeneous through the influx of foreign elements with different cultural backgrounds, possessing the potential to create disharmony within the previous culture. It can also create a harmonious hybridized society known as cultural amalgamation. In the United States, the term is often used to describe the cultural integration of immigrants to the country. A related concept has been defined as "cultural additivity."

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.