The Reform Acts (or Reform Bills, before they were passed) were legislation enacted in the United Kingdom in the 19th and 20th century to enfranchise new groups of voters and to redistribute seats in the House of Commons of the Parliament of the United Kingdom.

These began with the Reform Acts of 1832, 1867, and 1884, to increase the electorate for the House of Commons and remove certain inequalities in representation. The bill of 1832 disfranchised many boroughs which enjoyed undue representation and increased that of the large towns, at the same time extending the franchise. It was put through Parliament by the Whigs. The bill of 1867 was passed by the Conservatives under the urging of the Liberals, while that of 1882 was introduced by the Liberals and passed in 1884. These latter two bills provided for a more democratic representation.

Following the First World War, the Reform Act 1918 was enacted with cross-party unanimity. It enfranchised all men over the age of 21 and women over the age of 30. Ten years later, the Reform Act 1928, passed by the Conservatives, resulted in universal suffrage with a voting age of 21. In 1969, the United Kingdom became the first major democratic country to lower its age of franchise to 18 in the Reform Act 1969 passed by the Labour government.