former Canadian populist conservative political party, largely based in the western provinces.

The Canadian Alliance traced its roots to the Reform Party, which formed in 1987 as a populist and conservative expression of western Canadian frustration with the governing Progressive Conservative Party (Progressive Conservative Party of Canada) and previous governments led by the Liberal Party (Liberal Party of Canada). The Reform Party, based in Alberta and led by Preston Manning, a son of a former premier of that province, supported reducing the size of government and the public debt, though it favoured increased spending on the military and law enforcement. It opposed concessions by the federal government that would confer special status to French-speaking Quebec, and it generally rejected most rights claimed by cultural, aboriginal, and sexual minorities. The party's leader and many of its activists and followers were informed by religious conservatism, and from that came policies favouring traditional social values. Although the party was supported by some wealthy western Canadian business leaders, it had a populist dimension evident in suspicion of traditional party politics and support for instruments of direct democracy, both in its internal organization and for the entire political system.

In 1988 the Reform Party fielded candidates only in the western provinces, winning few votes and no federal parliamentary seats. In 1993, with the decimation of the Progressive Conservatives at the federal level—its representation shrank from 168 seats to 2—the Reform Party gained nearly one-fifth of the national vote and captured 52 seats, though all except one were constituencies in the western provinces. The Reform Party also won one-fifth of the votes in 1997, increasing its representation in the House of Commons to 60 and thereby becoming the official opposition to the ruling Liberal Party. However, the party's representation was still confined entirely to the west, and this prompted calls for it to unite with other conservatives in an attempt to oust the Liberal Party, which maintained a parliamentary majority with less than two-fifths of the national vote.

One attempt to eliminate destructive competition on the right led to the formation of the Canadian Reform Conservative Alliance in 2000. However, the new party, which became commonly known as the Canadian Alliance, was only marginally successful in extending its reach beyond the Reform Party base. The selection of Alberta's provincial treasurer, Stockwell Day, as leader reinforced the party's traditional western orientation, and Day's conservative stance on social issues—particularly his opposition to abortion and gay rights—further limited the party's appeal.

The Canadian Alliance won 25.5 percent of the national vote in 2000 and increased its contingent in the House of Commons to 66. Except for two seats won in Ontario, however, its parliamentary representation was again confined solely to the western provinces. Public support for the party dropped sharply following the election, and this provoked open revolt and the replacement of Day as leader with Stephen Harper. He attempted to balance the western interests that lay at the party's roots with the need to develop a national appeal, to mediate differences between moral and economic conservatives, and to hold together a force that was both a social movement and a political party. However, frustration at the inability of either the Alliance or the Progressive Conservatives to challenge the governing Liberals electorally led the two parties to merge in December 2003, when they formed the Conservative Party (Conservative Party of Canada).