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A two-party system (or monochrome government) is a form of party system where two major political parties dominate voting in nearly all elections, at every level. As a result, all, or nearly all, elected offices end up being held by candidates endorsed by one of the two major parties. Coalition governments occur only rarely in two-party systems.

Under a two-party system, one of the two parties typically holds a plurality in the legislature (or a legislative house in a bicameral system), and is referred to as the majority party. The smaller party is referred to as the minority party. Two-party systems are most common in polities with plurality vote counting system ("first past the post") to prevent the problem of two similar candidates "splitting" the same voters.

Notable examples of countries with two-party systems include the United States and Jamaica. Though these countries are often thought of as being two-party states, other parties may have small but significant bases of support and have seen candidates elected to local or subnational office.

Generally, a two-party system becomes a dichotomous division of the political spectrum with an ostensibly right-wing and left-wing party: Tories vs. Labour in some Commonwealth countries, Republicans vs. Democrats in the United States, and so on.

[edit] See also

• Duverger's law