An electoral system is a set of rules and mechanisms used to determine the results of an election. Electoral systems are used in politics to elect governments and also in non-political settings such as business, nonprofit organizations and informal organisations. These rules govern all aspects of the voting process: when elections occur, who is allowed to vote, who can stand as a candidate, how many votes are cast by each voter, how ballots are marked and cast, how the ballots are counted or weighed, how votes translate into the election outcome (seats), limits on campaign spending, and other factors affect the process. Political elections are defined by constitutions or electoral laws, and are typically conducted by election commissions, and may use one or more electoral systems for different offices.
Some electoral systems elect a single winner to a position, such as prime minister, president or governor, while others elect multiple winners, such as members of parliament or boards of directors. When electing a legislature, areas may be divided into constituencies with one or more representatives or the electorate may elect representatives as a single unit. Voters may vote directly for an individual candidate or for a list of candidates put forward by a political party or alliance. There are many variations in electoral systems.
The mathematical and normative study of voting rules falls under the branches of economics called social choice and mechanism design, but the question has also engendered substantial contributions from political scientists, analytic philosophers, computer scientists, and mathematicians. The field has produced several major results, including Arrow's impossibility theorem (showing that ranked voting cannot eliminate the spoiler effect) and Gibbard's theorem (showing it is impossible to design a straightforward voting system, i.e. one where it is always obvious to a strategic voter which ballot they should cast).
Types The most common categorizations of electoral systems are: single-winner vs. multi-winner systems; at-large contests versus district contests; and proportional representation vs. winner-take-all systems vs. mixed systems, which may combine a variety of election systems. As well, the formula used to determine the winners is critical - plurality (relative standings), majority of votes (50 percent plus 1), quota (a mathematically determined amount equal to less than the majority, such as used in single transferable voting), or some super-majority such as 60 percent.Britannica "Electoral system" https://www.britannica.com/topic/electoral-system accessed December 7, 2025
Single-winner and winner-take-all systems Where only a single winner is elected, the electoral system is winner-take-all. The same can be said for elections where only one person is elected per district. When district elections are winner-take-all, the electoral system as a whole may produce dis-proportional results. Where multiple winners are elected at once (in the same district), plurality block voting may elect members of just one party so may be considered winner-take-all.
In party block voting, voters can only vote for the list of candidates of a single party, with the party receiving the most votes winning all seats, even if that party receives only a minority of votes. This is also described as winner-take-all. This is used in five countries as part of mixed systems.
Plurality voting - first past the post and block voting
Plurality voting is a system in which the candidate(s) with the largest number of votes wins, with no requirement to get a majority of votes. In cases where there is a single position to be filled, it is known as first-past-the-post. This is the second-most-common electoral system for national legislatures (after proportional representation). Altogether at least 58 countries use FPTP and single-member districts to elect all or some of the members of a national-level legislative chamber,Table of Electoral Systems Worldwide IDEA the vast majority of which are current or former British colonies or U.S. territories. It is also the second-most-common system used for presidential elections, being used in 19 countries. The two-round system is the most common system used to elect a president.
In cases where there are multiple positions to be filled, most commonly in cases of multi-member constituencies, there are several types of plurality electoral systems. Under block voting (also known as multiple non-transferable vote or plurality-at-large), voters have as many votes as there are seats and can vote for any candidate, regardless of party, but give only one vote to each preferred candidate. The most-popular candidates are declared elected, whether they have a majority of votes or not and whether or not that result is proportional to the way votes were cast. Eight countries use this system.
Cumulative voting allows a voter to cast more than one vote for the same candidate, in multi-member districts. Its effect may be proportional to the same degree that single non-transferable voting or limited voting is, thus it is often called semi-proportional.
Approval voting is a choose-all-you-like voting system that aims to increase the number of candidates that win with majority support. Voters are free to pick as many candidates as they like and each choice has equal weight, independent of the number of candidates a voter supports. The candidate with the most votes wins.
Runoff systems
A runoff system is one in which a successful candidate is certain to receive a majority of votes to be elected, either in a runoff round with only two candidates or in a final round of vote counting if ranked votes are used. Runoff systems may ensure that a winner must have a majority of votes, but in some systems three or more candidates move on to the runoff election, in which case only a plurality is required in the last round.
Runoff systems are often called majoritarian systems, but in social choice theory, runoff systems are not called majority voting, as this term refers to Condorcet-methods.
There are two main groups of runoff systems, those in one group use a single round of voting achieved by voters casting ranked votes and then in successive rounds of counting, using vote transfers if necessary to establish a majority. Those in the other group have voters cast votes in two or more rounds of voting, to narrow the field of candidates and to determine a winner who has a majority of the votes. Both are primarily used for single-member constituencies or election of a single position such as mayor.
If a candidate receives a majority of the vote in the first round, then the system is simple first past the post voting. But if no one has a majority of votes in first round, runoff systems respond in different ways.
Under instant-runoff voting (IRV), when no one wins a majority in first round, runoff is achieved through vote transfers made possible by voters having ranked candidates in order of preference, with lower preferences used as back-up preferences. This system is used for parliamentary elections in Australia and Papua New Guinea. If no candidate receives a majority of the vote in the first round, the votes of the least-popular candidate are transferred as per marked second preferences and added to the totals of surviving candidates. This is repeated until a candidate achieves a majority. The count ends any time one candidate has a majority of votes. It may continue until only two candidates remain, at which point one or other of the candidates will take a majority of votes still in play.
A different form of single-winner preferential voting is the contingent vote where voters do not rank all candidates, but rank just two or three. The first preferences are counted. If no candidate has a majority in the first round, all candidates except the two with the most votes are excluded. If the voter gave first preference to one of the excluded candidates, the vote is transferred to the next usable back-up preferences if possible, or otherwise put in the exhausted pile. The canadidate who holds most of the resulting votes is the winner. With only two in the contest at the end, the winner holds a majority of the votes that are still in play. This system is used in Sri Lankan presidential elections, with voters allowed to mark three preferences.Sri Lanka: Election for President IFES
The other main form of runoff system is the two-round system, which is the most common system used for presidential elections around the world, being used in 88 countries. It is also used, in conjunction with single-member districts, in 20 countries for electing members of the legislature. If no candidate achieves a majority of votes in the first round of voting, a second round is held to determine the winner. In most cases the second round is limited to the top two candidates from the first round, although in some elections more than two candidates may choose to contest the second round; in these cases the second-round winner is not required to have a majority of votes, but may be elected by having a plurality of votes.
Some countries use a modified form of the two-round system, so going to a second round happens less often. In Ecuador a candidate in the presidential election is declared the winner if they receive more than 50 percent of the vote or 40% of the vote and are 10% ahead of their nearest rival,Ecuador: Election for President IFES In Argentina, where the system is known as ballotage, election is achieved by those with majority or if they have 40% and a 10% lead.
In some cases, where a certain level of support is required, a runoff may be held using a different system. In U.S. presidential elections, when no candidate wins a majority of the United States Electoral College (using seat count, not votes cast, as is used in the winner-take-all systems described above), a contingent election is held by the House of Representatives, not the voters themselves. The House contingency election sees three candidates go on to the last round and the Representatives of each state vote as a single unit, not as individuals, with the state's votes going to the plurality winner of the State members' votes.
An exhaustive ballot sees multiple rounds of voting (where no one has majority in first round). The number of rounds is not limited to two rounds, but sees the last-placed candidate eliminated in each round of voting, repeated until one candidate has majority of votes. Due to the potentially large number of rounds, this system is not used in any major popular elections, but is used to elect the Speakers of parliament in several countries and members of the Swiss Federal Council.
In some systems, such as election of the speaker of the United States House of Representatives, there may be multiple rounds held without any candidates being eliminated (unless by a candidate's own resignation) until a candidate achieves a majority.
Positional systems Positional systems like the Borda Count are ranked voting systems that assign a certain number of points to each candidate, weighted by position. The most popular such system is first-preference plurality. This system is intended to elect broadly acceptable options or candidates, rather than those preferred by a majority.Lippman, David. Voting Theory opentextbookstore.com This system is used to elect the ethnic minority representatives seats in the Slovenian parliament.
The Dowdall system is used in Nauru for parliamentary elections and sees voters rank the candidates. First preference votes are counted as whole numbers, the second preferences by two, third preferences by three, and so on; this continues to the lowest possible ranking.Nauru Parliament: Electoral system IPU The totals for each candidate determine the winners.
Multi-winner systems