An unconditional basic income (also called basic income, basic income guarantee, universal basic income, universal demogrant, or citizen’s income) is a form of social security system in which all citizens or residents of a country regularly receive an unconditional sum of money, either from a government or some other public institution, in addition to any income received from elsewhere.

An unconditional income transfer of less than the poverty line is sometimes referred to as a "partial basic income".

Basic income systems financed on returns to publicly owned enterprises (often then called Citizen's Dividend) are major components in many proposals for market socialism. Basic income schemes have also been promoted within the context of capitalist systems, which would be financed through taxation.

Similar proposals for "capital grants provided at the age of majority" date to Thomas Paine's Agrarian Justice of 1795, there paired with asset-based egalitarianism. The phrase "social dividend" was commonly used as a synonym for basic income in the English-speaking world before 1986, after which the phrase "basic income" gained widespread currency. Prominent advocates of the concept include Philippe Van Parijs, Ailsa McKay, André Gorz, Hillel Steiner, Peter Vallentyne, and Guy Standing.