Assimilation (from Latin assimilatio; "to render similar") may refer to:
- Assimilation (linguistics), a linguistic process by which a sound becomes similar to an adjacent sound
- Cultural assimilation, the process whereby a minority group gradually adapts to the customs and attitudes of the prevailing culture and customs.
- Assimilation (sociology), the blending or fusing of minority groups into the dominant society
- Linguistic assimilation (language shift), the progressive process whereby a speech community of a language shifts to speaking another language
- Americanization (of Native Americans), cultural assimilation of Native Americans in the United States
- Jewish assimilation
- Assimilation (biology) the conversion of nutrient into the fluid or solid substance of the body, by the processes of digestion and absorption
- Assimilation (meteorology), the process of objectively adapting the model state (of a numerical weather prediction model) to observations in a statistical optimal way taking into account model and observation errors
- Assimilation (psychology), incorporation of new concepts into existing schemes
- Assimilation effect, a frequently observed bias in social cognition