One man, one vote (or one person, one vote) is a slogan used by advocates of political equality through various electoral reforms such as universal suffrage, proportional representation, or the elimination of plural voting, malapportionment, or gerrymandering.
The British trade unionist George Howell used the phrase "one man, one vote" in political pamphlets in 1880.  During the 20th-century period of decolonisation and the struggles for national sovereignty, from the late 1940s onwards this phrase became widely used in developing countries where majority populations sought to gain political power in proportion to their numbers.[ citation needed]
In the United States, the "one person, one vote" principle was invoked in a series of cases in the 1960s.     [a] Applying the Equal Protection Clause of the United States Constitution, the Supreme Court majority opinion in Reynolds v. Sims (1964) ruled that state legislatures needed to redistrict in order to have congressional districts with roughly equal represented populations. In addition, the court ruled that, unlike the United States Congress, both houses of state legislatures needed to have representation based on districts containing roughly equal populations, with redistricting as needed after censuses. 
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This phrase was traditionally used in the context of demands for suffrage reform. Historically the emphasis within the House of Commons was on representing areas: counties, boroughs and, later on, universities. The entitlement to vote for the Members of Parliament representing the constituencies varied widely, with different qualifications over time, such as owning property of a certain value, holding an apprenticeship, qualifying for paying the local-government rates, or holding a degree from the university in question. Those who qualified for the vote in more than one constituency were entitled to vote in each constituency, while many adults did not qualify for the vote at all. Plural voting was also present in local government, whereby the owners of business property qualified for votes in the relevant wards.
Reformers argued that Members of Parliament and other elected officials should represent citizens equally, and that each voter should be entitled to exercise the vote once in an election. Successive Reform Acts by 1950 had both extended the franchise eventually to almost all adult citizens (barring convicts, lunatics and members of the House of Lords), and also reduced and finally eliminated most of the plural voting for both Westminster and local-government elections.
But, there were two significant exceptions:
The City of London had never expanded its boundaries and, with many residential dwellings being replaced by businesses, and the destruction of The Blitz, after the Second World War the financial district had barely five thousand residents altogether. The system of plural voting was retained for electing the City of London Corporation, with some modifications.
When Northern Ireland was established in 1921, it adopted the same political system then in place for the Westminster Parliament and British local government. But, the Parliament of Northern Ireland did not follow Westminster in changes to the franchise up to 1950. As a result, into the 1960s, plural voting was still allowed for both Parliament and local government. This meant that in local council elections only ratepayers and their spouses, whether renting or owning the property, could vote while company directors had an extra vote by virtue of their company's status. University representation continued at Stormont to 1969, while it was abolished for Westminster in 1948. Historians and political scholars have debated the extent to which the franchise for local government contributed to unionist electoral success in controlling councils in nationalist-majority areas. 
Based on a number of inequities, the Northern Ireland Civil Rights Association was founded in 1967. It had five primary demands, and added the demand that each citizen in Northern Ireland be afforded the same number of votes for local elections (national elections followed the same eligibility rules as the rest of the UK). The slogan "one man, one vote" became a rallying cry for this campaign.[ citation needed] The Parliament of Northern Ireland voted to update the voting rules, which were implemented for the Northern Ireland general election, 1969.
The United States Constitution requires a decennial census for the purpose of assuring fair apportionment. Reapportionment has generally been conducted without incident with the exception of the reapportionment that should have followed the 1920 Census was effectively skipped pending resolution by the Reapportionment Act of 1929. Congressional seats have been reapportioned based on population changes between states. State legislatures initially established election of congressional representatives from districts, often based on traditional counties or parishes which preceded founding of the new government. The question arose as to whether the state legislatures were required to ensure that congressional districts were roughly equal in population and to draw new districts to accommodate demographic changes.  
Some states redrew their U.S. House districts every ten years to reflect changes in population patterns; many did not. Some never redrew them, except when it was mandated by a change in the number of seats to which that state was entitled in the House of Representatives. In many states, this led to a skewing of influence for voters in some districts over those in others. For example, if the 2nd congressional district eventually had a population of 1.5 million, but the 3rd had only 500,000, then, in effect — since each district elected the same number of representatives — a voter in the 3rd district had three times the voting "power" of a 2nd-district voter. Alabama's state legislature resisted redistricting from 1910 to 1972 (when forced by federal court order). As a result, rural residents retained a wildly disproportionate amount of power in a time when other areas of the state became urbanized and industrialized, attracting greater populations. Such urban areas were under-represented in the state legislature and underserved; their residents had difficulty getting needed funding for infrastructure and services. They paid far more in taxes to the state than they received in benefits in relation to the population. 
The Constitution includes the result of the Great Compromise resulting in representation for the US Senate. Each state was equally represented in the Senate with two representatives, without regard to population. The Founding Fathers considered this principle of such importance that they included a clause in the Constitution to prohibit any state from being deprived of equal representation in the Senate without its permission; see Article V of the United States Constitution. For this reason, "one person, one vote" has never been implemented in the U.S. Senate, in terms of representation by states.
When states established their legislatures, they often adopted a bicameral model based on colonial governments. Many copied the Senate principle, establishing an upper house based on geography - for instance a state senate with one representative drawn from each county. By the 20th century, this often led to state senators having widely varying amounts of power, with ones from rural areas having votes equal to senators representing much greater urban populations.
Activism in the Civil Rights Movement to regain the ability of African Americans in the South to register and vote highlighted other voting inequities across the country. Numerous court challenges were raised, including in Alabama due to the lack of reapportionment, for decades.
In Colegrove v. Green, 328 U.S. 549 (1946) the United States Supreme Court held in a 4-3 plurality decision that Article I, Section 4 left to the legislature of each state the authority to establish the time, place, and manner of holding elections for representatives.
However, in Baker v. Carr, 369 U.S. 186 (1962) the United States Supreme Court overturned the previous decision in Colegrove holding that malapportionment claims under the Equal Protection Clause of the Fourteenth Amendment were not exempt from judicial review under Article IV, Section 4, as the equal protection issue in this case was separate from any political questions. 
The "one person, one vote" doctrine, which requires electoral districts to be apportioned according to population, thus making each district roughly equal in population, was further cemented in the cases that followed Baker, including Gray v. Sanders, 372 U.S. 368 (1963) which concerned state county districts, Reynolds v. Sims, 377 U.S. 533 (1964) which concerned state legislature districts, Wesberry v. Sanders, 376 U.S. 1 (1964) which concerned U.S. Congressional districts and Avery v. Midland County, 390 U.S. 474 (1968) which concerned local government districts, a decision which was upheld in Board of Estimate of City of New York v. Morris, 489 U.S. 688 (1989).  Evenwel v. Abbott, 578 U.S. ___ (2016) said states may use total population in drawing districts.
- In Alaska, when an initiative for instant runoff voting (IRV) was put on the ballot in 2002, League of Women Voters President Cheryl Jebe said, "It appears to compromise the well-established principle of one person, one vote, established by the United States Supreme Court." 
- But, in 1975, a Michigan court ruling declared that "majority preferential voting," as IRV was then known, did not violate the one-man, one-vote rule: 
Under the 'M.P.V. System', however, no one person or voter has more than one effective vote for one office. No voter's vote can be counted more than once for the same candidate. In the final analysis, no voter is given greater weight in his or her vote over the vote of another voter, although to understand this does require a conceptual understanding of how the effect of a 'M.P.V. System' is like that of a run-off election. The form of majority preferential voting employed in the City of Ann Arbor's election of its Mayor does not violate the one-man, one-vote mandate nor does it deprive anyone of equal protection rights under the Michigan or United States Constitutions.
- The courts have found that special-purpose districts must also follow the one person, one vote rule.         
The term "One man, one vote, once" has been applied to Rhodesia (now Zimbabwe), Zambia, and Angola, where elections were successfully held that were relatively free of corruption and violence, but then a strongman took hold and free voting ended.  
- One vote, one value - a similar principle in Australia
- Proportional representation
- Panachage - an opposite system
- George Howell (1880). "One man, one vote". Manchester Selected Pamphlets. JSTOR 60239578
- Peter Duignan; Lewis H. Gann (1991). Hope for South Africa?. Hoover Institution Press. p. 166. ISBN 0817989528.
- Bond, Larry; Larkin, Patrick (June 1991). Vortex. United States: Little, Brown and Warner Books. p. 37. ISBN 0-446-51566-3. OCLC 23286496.
- Boam, Jeffrey (July 1989). Lethal Weapon 2. Warner Bros.
- Richard H. Fallon, Jr. (2013). The Dynamic Constitution. Cambridge University Press, 196.
- Douglas J. Smith (2014). On Democracy's Doorstep: The Inside Story of How the Supreme Court Brought "One Person, One Vote" to the United States. Farrar, Straus and Giroux.
- "One person, one vote", in David Andrew Schultz (2010). Encyclopedia of the United States Constitution. Infobase Publishing, 526.
- Stephen Ansolabehere, James M. Snyder (2008). The End of Inequality: One Person, One Vote and the Transformation of American Politics. Norton.
- C. J. Warren, Reynolds v. Sims, 377 U.S. 533, 558 (1964) (quoting Gray v. Sanders, 372 U.S. 368 (1963)), cited in "One-person, one-vote rule", Legal Information Institute, Cornell University Law School.
- Charlie B. Tyler, "County Government in the Palmetto State", University of South Carolina, 1998, p. 221
- John H. Whyte. "'How much discrimination was there under the unionist regime, 1921-1968?'". Conflict Archive on the Internet. Retrieved 2007-08-30.
- "The Supreme Court: One-Man, One-Vote, Locally". Time. 1968-04-12. Retrieved 2010-05-20.
- FairVote - In the news
- Stephenson v Ann Arbor Board of Canvassers, fairvote.org, accessed 6 November 2013.
- Avery v. Midland County, 390 U.S. 474, 88 S. Ct. 1114, 20 L. Ed. 2d 45 (1968)
- Ball v. James, 451 U.S. 355, 101 S. Ct. 1811, 68 L. Ed. 2d 150 (1981)
- Bjornestad v. Hulse, 229 Cal. App. 3d 1568, 281 Cal. Rptr. 548 (1991)
- Board of Estimate v. Morris, 489 U.S. 688, 109 S. Ct. 1433, 103 L. Ed. 2d 717 (1989)
- Hadley v. Junior College District, 397 U.S. 50, 90 S. Ct. 791, 25 L. Ed. 2d 45 (1970)
- Hellebust v. Brownback, 824 F. Supp. 1511 (D. Kan. 1993)
- Kessler v. Grand Central District Management Association, 158 F.3d 92. (2d Cir. 1998)
- Reynolds v. Sims, 377 U.S. 533, 84 S. Ct. 136, 12 L. Ed. 2d 506 (1964)
- Salyer Land Co. v. Tulare Lake Basin Water Storage District, 410 U.S. 719 (1973)
- W. Martin James III (2011). A Political History of the Civil War in Angola: 1974-1990. Transaction Publishers. p. X. ISBN 9781412815062.