A progressive tax is a tax in which the tax rate increases as the taxable amount increases. The term progressive refers to the way the tax rate progresses from low to high, with the result that a taxpayer's average tax rate is less than the person's marginal tax rate. The term can be applied to individual taxes or to a tax system as a whole. Progressive taxes are imposed in an attempt to reduce the tax incidence of people with a lower ability to pay, as such taxes shift the incidence increasingly to those with a higher ability-to-pay. The opposite of a progressive tax is a regressive tax, such as a sales tax, where the poor pay a larger proportion of their income compared to the rich (for example, spending on groceries and food staples varies little against income, so poor pay similar to rich even while latter has much higher income).

The term is frequently applied in reference to personal income taxes, in which people with lower income pay a lower percentage of that income in tax than do those with higher income. It can also apply to adjustments of the tax base by using tax exemptions, tax credits, or selective taxation that creates progressive distribution effects. For example, a wealth or property tax, a sales tax on luxury goods, or the exemption of sales taxes on basic necessities, may be described as having progressive effects as it increases the tax burden of higher income families and reduces it on lower income families.

Progressive taxation is often suggested as a way to mitigate the societal ills associated with higher income inequality, as the tax structure reduces inequality; economists disagree on the tax policy's economic and long-term effects. One study suggests progressive taxation is positively associated with subjective well-being, while overall tax rates and government spending are not.

In the early days of the Roman Republic, public taxes consisted of assessments on owned wealth and property. For Roman citizens, the tax rate under normal circumstances was 1% of property value, and could sometimes climb as high as 3% in situations such as war. These taxes were levied against land, homes and other real estate, slaves, animals, personal items and monetary wealth. By 167 BC, Rome no longer needed to levy a tax against its citizens in the Italian peninsula, due to the riches acquired from conquered provinces. After considerable Roman expansion in the 1st century, Augustus Caesar introduced a wealth tax of about 1% and a flat poll tax on each adult; this made the tax system less progressive, as it no longer only taxed wealth. In India under the Mughal Empire, the Dahsala system was introduced in A.D. 1580 under the reign of Akbar. This system was introduced by Akbar's finance minister, Raja Todar Mal, who was appointed in A.D. 1573 in Gujarat. The Dahsala system is a land-revenue system (system of taxation) which helped to make the collecting system be organised on the basis of land fertility.

The first modern income tax was introduced in Great Britain by Prime Minister William Pitt the Younger in his budget of December 1798, to pay for weapons and equipment for the French Revolutionary War. Pitt's new graduated (progressive) income tax began at a levy of 2 old pence in the pound (1⁄120 or 0.83%) on annual incomes over £60 and increased up to a maximum of 2 shillings (10%) on incomes of over £200. Pitt hoped that the new income tax would raise £10 million, but actual receipts for 1799 totalled just over £6 million.

Pitt's progressive income tax was levied from 1799 to 1802 when it was abolished by Henry Addington during the Peace of Amiens. Addington had taken over as prime minister in 1801, after Pitt's resignation over Catholic emancipation. The income tax was reintroduced by Addington in 1803 when hostilities recommenced, but it was again abolished in 1816, one year after the Battle of Waterloo.

The present form of income tax in the United Kingdom was reintroduced by Sir Robert Peel in the Income Tax Act 1842. Peel, as a Conservative, had opposed income tax in the 1841 general election, but a growing budget deficit required a new source of funds. The new income tax, based on Addington's model, was imposed on incomes above £150. Although this measure was initially intended to be temporary, it soon became a fixture of the British taxation system. A committee was formed in 1851 under Joseph Hume to investigate the matter but failed to reach a clear recommendation. Despite the vociferous objection, William Gladstone, Chancellor of the Exchequer from 1852, kept the progressive income tax, and extended it to cover the costs of the Crimean War. By the 1860s, the progressive tax had become a grudgingly accepted element of the English fiscal system.

In the United States, the first progressive income tax was established by the Revenue Act of 1862. The act was signed into law by President Abraham Lincoln, and replaced the Revenue Act of 1861, which had imposed a flat income tax of 3% on annual incomes above $800. The Sixteenth Amendment to the United States Constitution, adopted in 1913, permitted Congress to levy all income taxes without any apportionment requirement. By the mid-20th century, most countries had implemented some form of progressive income tax.