Reform Acts or Reform Bills, in British history, name given to three major measures that liberalized representation in Parliament in the 19th cent. Representation of the counties and boroughs in the House of Commons had not, except for the effects of parliamentary union with Scotland (1707) and Ireland (1800), been materially altered since the 17th cent. The system was very irregular and greatly restricted the franchise; it failed to take into account the great shifts of population and the growth of new social classes that attended the Industrial Revolution. "Pocket boroughs," controlled by the crown or large landholders, and "rotten boroughs," whose populations had declined (the most notorious was Old Sarum, which had virtually ceased to exist) were amply represented. Yet large cities such as Manchester and Birmingham returned no members of their own. Out of a population of about 24,000,000 in the British Isles (including Ireland), only about 435,000 were qualified to vote. Corruption and the sale of seats flourished. Reform agitation, beginning to develop in the 1760s, was supported by William Pitt and others, but the emergency period of the French Revolution interrupted it. Revived c.1807, it had become the leading issue of the day by 1830.

The Reform Act of 1832, enacted under the Whig administration of the 2d Earl Grey, redistributed seats in the interest of larger communities; it also extended the franchise in the boroughs to those who occupied premises of an annual value of £10 and in the counties to similar leaseholders—to the advantage of shopkeepers and other middle-class men—and it simplified registration and voting procedure. The bill was passed in the House of Lords only as a result of the government's threat to overcome opposition by creating enough Whig peers to ensure passage. The electorate was increased by about 50%, but the new distribution of seats still allowed the rural areas to retain their supremacy.

Agitation by the advocates of Chartism and others for further reform produced no results until Benjamin Disraeli made a bid for the support of the working classes by enacting the Reform Act of 1867. This act, which further redistributed the seats and more than doubled the electorate, gave the vote to many workingmen in the towns. The Reform Act of 1884, passed during the administration of William Gladstone, removed the distinction between county and borough franchises and, by the reduction of rural qualifications, added about 2,000,000 more men to the electorate. A redistribution act in 1885 rendered representation nearly proportional to population. It was not, however, until the passage of the Representation of the People Acts in the 20th cent. that the British Parliament adopted universal male and female suffrage.