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. Historically, it is often used to describe the cultural integration of immigrants to the United States. A related concept has been defined as "cultural additivity."

The melting-together metaphor was in use by the 1780s. The exact term "melting pot" came into general usage in the United States after it was used as a metaphor describing a fusion of nationalities, cultures and ethnicities in the 1908 play of the same name.

The desirability of assimilation and the melting pot model has been rejected by proponents of multiculturalism, who have suggested alternative metaphors to describe the current American society, such as a salad bowl, or kaleidoscope, in which different cultures mix, but remain distinct in some aspects. The melting pot continues to be used as an assimilation model in vernacular and political discourse along with more inclusive models of assimilation in the academic debates on identity, adaptation and integration of immigrants into various political, social and economic spheres.