A constituency is any cohesive corporate unit or body bound by shared structures, goals or loyalty. It can be used to describe a business's customer base and shareholders, or a charity's donors or those it serves. The most common meaning of constituency occurs in politics and means the group of people or geographical area that a particular elected representative or group of elected representatives represents. The rest of this article deals with this sense of constituency.
Specifically, a constituency often refers to the group or area from which voters in an election are drawn. Depending on the electoral system being used, a constituency may elect one or more members. For instance, in the United Kingdom, Westminster Parliamentary constituencies each elect one Member of Parliament using a first past the post system (though some used to elect more than one), while the larger European Parliamentary constituencies each elect a number of Member of the European Parliament (see 'Regions of England').
Constituencies in the Republic of Ireland elect between three and five TDs, while constituencies between 1536 and 1800 in the Kingdom of Ireland used to return two MPs. Northern Ireland constituencies elects six MLAs to the Northern Ireland Assembly.
In the United Kingdom, a parliamentary constituency is sometimes called a Parliamentary seat or a Division. Constituencies for local government elections are called Wards. (The article 'MPs elected in the UK general election, 2001' includes the constituencies as they stood at the last general election.)
In the United States, U.S. Supreme Court decisions require the equalization of populations of constituencies after each decennial census. This requirement opens up the possibility of gerrymandering for political or factional advantage. A Pennsylvania legislator long active in redistricting issues, State Rep. Mark B. Cohen of Philadelphia, said that "In election years, constituents choose their legislative officials. In redistricting years, legislative officials usually try to choose their future constituents."
A marginal constituency is one where the margin between the expected voting for the major parties in an election is slim. In United Kingdom general elections, the voting in a relatively small number of marginal constituencies usually determines the outcome of the entire election.
In the United States, electoral constituencies are known as congressional districts. In Canada, they are known as ridings for Members of Parliament and constituencies for Members of Legislative Assemblies at the provincial level. In Australia, federal and state constituencies are known as electorates or seats. In France, electoral constituencies are known as circonscriptions électorales.
Marginal constituencies are also known as: