"Crossing the floor" means to leave one's political party and join another, or in a more general sense, to vote against one's own party.

It originates in the British House of Commons where, as in the Canadian version, the government and opposition face each other and a member might physically cross the floor to join an opposing party. However, the term now applies to any political defection, now matter how the seats are arranged.

Some notable floor crossings in Canadian history:

Current government

It didn't take Stephen Harper and the newly elected Conservative government long to snag a floor crosser: they managed it before Parliament even began sitting. Harper surprised Ottawa watchers by appointing David Emerson as trade minister on Feb. 6, 2006, the day the government was sworn in. Up until an hour or so earlier – when Paul Martin officially handed in the resignation of his government – Emerson had been the Liberal industry minister.

During the election campaign, Emerson had promised to be a thorn in Harper's side if the Conservatives formed a government.

In January 2007, a day after Harper shuffled his cabinet, Wajid Khan, MP for Mississauga-Streetsville in Ontario, crossed the floor from the Liberals to join the Conservatives. A month later, on Feb. 6, ex-Tory Garth Turner, who had been sitting as an Independent, decided to join the Liberals. Turner is from the Ontario riding of Halton.

Joe Comuzzi, the Thunder Bay, Ont., MP who left the Liberal cabinet in 2005 to vote against the government's same-sex marriage bill and who was kicked out of the party in March 2007 for supporting the Tory budget, joined the Conservatives in June.

After Belinda Stronach crossed the floor to join the Liberals in 2005, Harper said his party would not go out of its way to encourage MPs to cross the floor.

"We are trying to create a principled party where people act in a principled way, and obviously we're fairly cautious about encouraging party jumping, because that's the kind of thing that generates cynicism."

Ethics commissioner Bernard Shapiro investigated the courting of Emerson and found that no rules were broken when Harper persuaded the former Liberal to join the Conservatives – but Shapiro called on Parliament to hold a debate on the subject of switching parties.

Paul Martin's Liberal Government

Transport Minister Jean Lapierre started out as a Liberal in the 1979 election, but left the party in 1990 to sit as an Independent, then sat with the Bloc Québécois for two years. He then left federal politics for about 10 years before returning as a Liberal in the 2004 election.

In May 2003, Scott Brison was a contender for the leadership of the Progressive Conservative party, and said he wanted to build "a competitive conservative alternative" to the Liberals. In December 2003, Brison left the PCs before their amalgamation into the new Conservative party, saying it would not reflect his values. He joined the Liberals and later became the minister of public works and government services.

In January 2004, Keith Martin, who once ran for the leadership of the Canadian Alliance, announced he would sit as an Independent. He won his B.C. seat in the 2004 election as a Liberal.

Paul Martin welcomes Belinda Stronach into the Liberal party. (CP photo)

In 2004, Belinda Stronach came second in the leadership race for the Conservative party. On May 17, 2005, Stronach left the party and joined Paul Martin's Liberal cabinet, as minister of human resources and skills development. Two days later, her vote was instrumental in keeping Paul Martin's minority Liberal government alive. The vote on a budget amendment ended in a tie, broken by the Speaker in favour of the government.

All four of these members were re-elected in the 2006 election, although they'll now sit in Opposition.

The DRC-PC coalition

In May 2001, several members of the Canadian Alliance were suspended from their caucus and later sat as the Democratic Representative Caucus. The DRC and the Progressive Conservatives formed a coalition in September 2001. The coalition ended in April 2002, after Stephen Harper won the party leadership, and most of the members returned to the Canadian Alliance. Inky Mark, however, stayed with the Progressive Conservatives.

The Bloc Québécois

From May to July 1990, several Quebec members of the Progressive Conservatives, including cabinet minister Lucien Bouchard, left the party to sit as independent MPs. They formed the Bloc Québécois in December 1990.

The man no one wanted

Robert Toupin, who had worked for the Liberal party in Quebec, joined the Progressive Conservatives for the 1984 election. When he left the PCs to sit as an Independent, the Liberal association in his Montreal-area riding made it clear they didn't want him. He joined the NDP seven months later as its lone Quebec member in the House. In 1987, he left the NDP, alleging that communists had infiltrated the party. He was then invited to join the Rhinoceros party.

Belinda, take note

Jack Horner, who had lost the leadership race for the Progressive Conservatives in 1976, crossed the floor in April 1977 to join the Liberal cabinet. He lost his seat in the 1979 election.

Paul Hellyer lost the leadership of the Liberal party in 1968 to Pierre Trudeau. He crossed the floor to the PCs in 1972, lost his seat in 1974 and subsequently lost the race to lead the Tories.

The Unionist party

The Conscription Crisis of 1917 saw many Liberals, especially those from English Canada, cross the floor to join Robert Borden's Unionist party for the 1917 general election. Liberals who remained in the Opposition, mainly from Quebec, were dubbed Laurier Liberals, after their leader, Wilfrid Laurier.

The beginning

The first floor-crossing in the federal government was that of Stewart Campbell, who, in 1868, left Nova Scotia's Anti-Confederation party to sit with the Liberal-Conservatives of John A. Macdonald. The Anti-Confederation party dissolved in January 1869 and members joined other federal parties.

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