Wikipedia: First-past-the-post election system

An election voting system for single-member districts, variously called first-past-the-post, plurality voting, or relative majority. This system is widely used at all levels of politics - famously in Great Britain and the United States. For a thorough list, see below.

Voting

Each voter selects one candidate.

Counting the Votes

All votes are counted and the candidate (or proposal) with the most votes is declared the winner.

An Example

4 candidates: Andrea, Brad, Carter, and Delilah.

35 voters choose Andrea
27 voters choose Brad
16 voters choose Carter
11 voters choose Delilah

Andrea is elected with the most votes.

Potential for Tactical Voting

There is enormous potential for tactical voting. Voters only get one chance to express their preference, so if they express it for a candidate who stands little chance of winning, they do not get to choose between the popular candidates. Because of this, most voters vote for the candidate they prefer among those candidates who they believe have a chance of winning. Therefore, candidates often vie to seem like they are likely to win, rather than that they are preferable.

To counteract tactical voting, sometimes groups of similar-minded voters will hold preliminary, or primary, elections amongst themselves to choose a candidate for the true election. This ensures that their vote will not be split amongst similar candidates. Sometimes this is institutionalized in the form of a political party.

Another potential downfall of this system is that the winner does not have a majority, and in fact often does not. Possible solutions to this problem is found in runoff voting and instant runoff voting.

Where it's used

Countries that use this system to elect the lower or only house of their legislature:

Bahamas -- Bangladesh -- Barbados -- Belize -- Botswana -- Canada -- Dominica -- Gambia -- Grenada -- Jamaica -- Federated States of Micronesia -- Nepal -- New Zealand -- Papua New Guinea -- Saint Kitts and Nevis -- Saint Lucia -- Saint Vincent and the Grenadines -- Samoa -- Solomon Islands -- Trinidad and Tobago -- United Kingdom -- United States -- Zambia

Source: Making Votes Count, Gary Cox (1997)

What the critics say

Critics of the system argue that it can lead to under-representation, and government by minority. If there are three candidates in an election, it is possible for the winner to have received only one more vote than his or her competitors, and thus two thirds of the electorate have voted against the winner. This system also discourages individuals from voting for smaller political parties who they might otherwise support, because their votes will effectively not count in the final tally. This aspect of the system has been cited as both an advantage and a disadvantage.

If the system has multiple areas, such as the states in the electoral college system for the US presidential elections, or constituencies for the UK parliamantary elections, the system favors political parties with concentrated geographical support, as they can command the majority in that area. This facet of the system, led to the practice of gerrymandering, which is the drawing of electoral district boundaries for the purpose of influencing an election.

In the UK, there were two majority governments in the 20th century.