The electoral threshold, or election threshold, is the minimum share of votes that a candidate or political party requires before they become entitled to representation or additional seats in a legislature.

This limit can operate in various ways; for example, in party-list proportional representation systems where an electoral threshold requires that a party must receive a specified minimum percentage of votes (e.g. 5%), either nationally or in a particular electoral district, to obtain seats in the legislature. In single transferable voting, the election threshold is called the quota, and it is possible to achieve it by receiving first-choice votes alone or by a combination of first-choice votes and votes transferred from other candidates based on lower preferences. It is also a common occurrence to see someone elected with less than the quota in STV.

In mixed-member-proportional (MMP) systems, the election threshold determines which parties are eligible for top-up seats in the legislative chamber. Some MMP systems still allow a party to retain the seats they won in electoral districts even when they did not meet the threshold nationally; in some of these systems, top-up seats are allocated to parties that do not achieve the electoral threshold if they have won at least one district seat or have met some other minimum qualification.

The effect of this electoral threshold is to deny representation to small parties or to force them into coalitions. Such restraint is intended to make the election system more stable by keeping out fringe parties. Proponents of a stiff electoral threshold say that having a few seats in a legislature can significantly boost the profile of a party and that providing representation and possibly veto power for a party that receives only 1 percent of the vote is not appropriate. However, others argue that in the absence of a ranked ballot or proportional voting system at the district level, supporters of minor parties, barred from top-up seats, are effectively disenfranchised and denied the right to be represented by someone of their choosing.

Two boundaries can be defined – a threshold of representation (or threshold of inclusion) is the minimum vote share that might yield a party a seat under the most favorable circumstances for the party, while the threshold of exclusion is the maximum vote share that could be insufficient to yield a seat under the least favorable circumstances. Arend Lijphart suggested calculating the informal threshold as the mean of these. Michael Gallagher gave this value the name effective threshold and set it at 75 percent of the Droop quota. However, he warned that this was to be used at the district level and not to assume that a party with a certain share of the overall vote was sure to have representation.

The electoral threshold is a barrier to entry for political parties to the political competition. But some barrier to entry is seen in any system, due to the effective threshold produced by district magnitude (DM) and due to the effect of wasted votes caused by the election system being used. For instance, under first past the post election system, only one party can win the one seat in a district, and all others are not elected, whether one of them has 49 percent of the vote or the winner has just 20 percent of the vote. In very proportional election systems, each member is elected by about the same number of votes (approximately equivalent to the Hare quota if there are very few wasted votes), and anything less than that number is insufficient to receive representation. In systems where DM varies from district to district, a district with exceptionally high district magnitude, such as may be used in the largest city, may allow representation to small parties that do not have a chance for any representation at all in other districts where DM is low. Conversely, where many districts are used (and thus average DM is low), the effective threshold for a party to potentially take at least one seat is also low.

The Parliamentary Assembly of the Council of Europe recommends for parliamentary elections a threshold not higher than three percent.

For single transferable vote, to produce representation for parties with approximately ten percent or more of the overall vote, John M. Carey and Simon Hix recommended a district magnitude (DM) of approximately six or more. Support for a party is not homogeneous across an electorate, so a party with ten percent of the vote is expected to easily achieve the electoral threshold in at least one district even if not in others. Most STV systems used today use the Droop quota, which in a six-member district is 14 percent of the votes cast in the district. Carey and Hix note that increasing the DM from one to six produces an improvement in proportionality that is much higher than any subsequent increase in DM, pointing out that the most popular parties take the largest share of votes and the largest share of seats in any PR system, leaving few to small parties under any system. Transfers of votes from other parties to a party and willingness of the party's voters to mark alternate preferences (and thus prevent their vote from being exhausted) also play a role in the amount of representation that each party takes, and is somewhat independent of the party's vote share in the first count. Due to the effect of districting, a party is not assured of taking its proportional share of seats, but with the use of districts with a DM of 6, it is expected that a party with more than ten percent of the overall vote will elect at least one member, according to Carey and Hix.^{[citation needed]}