Large parts of the world routinely use more than one language. Bilingualism is the ability to comprehend and produce two languages with functional proficiency, whether acquired in early childhood or later.

Bilinguals may keep their languages for different domains or switch within a single conversation. Perfect balance is uncommon; dominance often shifts across the lifespan. Research on attention and cognitive control in bilinguals continues, with nuanced rather than simple findings.

Societies institutionalize bilingualism through schools, official-language policy, and media. Individuals experience it as resource and sometimes as a site of prejudice. Linguists study code choice, transfer, and identity to understand how two systems coexist in one mind and one community.

• Functional ability in two languages
• May be early or late, balanced or dominant
• Involves domain use and switching
• Shaped by policy, identity, and cognition