A tax that governments impose on financial income generated by all entities within their jurisdiction. By law, businesses and individuals must file an income tax return every year to determine whether they owe any taxes or are eligible for a tax refund. Income tax is a key source of funds that the government uses to fund its activities and serve the public.

Most countries employ a progressive income tax system in which higher income earners pay a higher tax rate compared to their lower earning counterparts.

The first income tax imposed in America was during the War of 1812. Its original purpose was to fund the repayment of a $100 million debt that was incurred through war-related expenses. After the war, the tax was repealed, but income tax became permanent during the early 20th century.