In economics, a negative income tax (NIT) is a system which reverses the direction in which tax is paid for incomes below a certain level; in other words, earners above that level pay money to the state while earners below it receive money, as shown by the blue arrows in the diagram. NIT was proposed by Juliet Rhys-Williams while working on the Beveridge Report in the early 1940s and popularized by Milton Friedman in the 1960s as a system in which the state makes payments to the poor when their income falls below a threshold, while taxing them on income above that threshold. Together with Friedman, supporters of NIT also included James Tobin, Joseph A. Pechman, and Peter M. Mieszkowski, Jim Gray and even then-President Richard Nixon, who suggested implementation of modified NIT in his Family Assistance Plan. After the increase in popularity of NIT, an experiment sponsored by the US government was conducted between 1968 and 1982 on effects of NIT on labour supply, income, and substitution effects.

Dame Juliet Evangeline Rhys-Williams, Lady Rhys-Williams, was a British writer and politician who was successively a member of the Liberal National Party, the Liberal Party and the Conservative Party.