One man, one vote in the context of Mississippi Freedom Democratic Party

Universal suffrage or universal franchise refers to the right to vote being available for all adults within a jurisdiction. The idea is often endorsed by the slogan "one man, one vote".

For many, the term universal suffrage assumes the exclusion of the young and non-citizens (among others). At the same time, some insist that more inclusion is needed before suffrage can be truly universal. Democratic theorists, especially those hoping to achieve more universal suffrage, support presumptive inclusion, where the legal system would protect the voting rights of all subjects unless the government can clearly prove that disenfranchisement is necessary. Universal full suffrage includes both the right to vote, also called active suffrage, and the right to be elected, also called passive suffrage.

Universal manhood suffrage is a form of voting rights in which all adult male citizens within a political system are allowed to vote, regardless of income, property, religion, race, or any other qualification. It is sometimes summarized by the slogan, "one man, one vote".

Apportionment is the process by which seats in a legislative body are distributed among administrative divisions, such as states or parties, entitled to representation. This page presents the general principles and issues related to apportionment. The apportionment by country page describes the specific practices used around the world. The Mathematics of apportionment page describes mathematical formulations and properties of apportionment rules.

The simplest and most universal principle is that elections should give each vote an equal weight. This is both intuitive and stated in laws such as the Fourteenth Amendment to the United States Constitution (the Equal Protection Clause).

The participation criterion is a voting system criterion that says candidates should never lose an election as a result of receiving too many votes in support. More formally, it says that adding more voters who prefer Alice to Bob should not cause Alice to lose the election to Bob.

Voting systems that fail the participation criterion exhibit the no-show paradox, where a voter is effectively disenfranchised by the electoral system because turning out to vote could make the result worse for them; such voters are sometimes referred to as having negative vote weights, particularly in the context of German constitutional law, where courts have ruled such a possibility violates the principle of one man, one vote.

The highest averages, divisor, or divide-and-round methods are a family of apportionment rules, i.e. algorithms for fair division of seats in a legislature between several groups (like political parties or states). More generally, divisor methods are used to round shares of a total to a fraction with a fixed denominator (e.g. percentage points, which must add up to 100).

The methods aim to treat voters equally by ensuring legislators represent an equal number of voters by ensuring every party has the same seats-to-votes ratio (or divisor). Such methods divide the number of votes by the number of votes per seat to get the final apportionment. By doing so, the method maintains proportional representation, as a party with e.g. twice as many votes will win about twice as many seats.