More of the world’s population uses more than one language than monolingual surveys sometimes suggest. Bilingualism is the ability to comprehend and produce two languages with functional proficiency, whether acquired from early childhood or later in life.

Bilinguals may use their languages in different domains—home, school, work—or switch within a single conversation. Proficiency need not be perfectly balanced; dominance in one language is common and can shift over the lifespan. Cognitive research has explored attention and control advantages linked to managing two systems, though findings remain nuanced.

Societies institutionalize bilingualism through education policy, official-language laws, and media. Individuals experience bilingualism as both resource and, at times, site of discrimination. Linguists study code choice, transfer, and identity to understand how two languages coexist in one mind and one community.

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