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Process of drawing electoral district boundaries in the United States
the process of determining electoral boundaries in the United States

Redistricting in the United States is the process of drawing electoral district boundaries. For the United States House of Representatives, and state legislatures, redistricting occurs after each decennial census. The U. S. Constitution in Article 1, Section 2, Clause 3 provides for proportional representation in the House of Representatives. The Reapportionment Act of 1929 required that the number of seats in the U. S. House of Representatives be kept at a constant 435, and a 1941 act made the reapportionment among the states by population automatic after every decennial census. Reapportionment occurs at the federal level followed by redistricting at the state level. According to , Article I, Section 4 left to the legislature of each state the authority to establish congressional districts; however, such decisions are subject to judicial review. In most states redistricting is subject to political maneuvering, but some state legislatures have created independent commissions. The Uniform Congressional District Act (enacted in 1967) requires that representatives be elected from single member districts. When a state has a single representative, that district will be state wide. Gerrymandering in the redistricting process has been a problem since the early days of the republic. In recent years, critics have argued that redistricting has been used to neutralize minority voting power. Supporters say it enhances electoral competitiveness.

Six states have a single representative in the United States House of Representatives, because of their low populations. These are Alaska, Delaware, North Dakota, South Dakota, Vermont, and Wyoming. These states do not need redistricting for the House and elect members on a state wide at large basis. In 25 states, the state legislature has primary responsibility for creating a redistricting plan, in many cases subject to approval by the state governor. To reduce the role that legislative politics might play, thirteen states (Alaska, Arizona, California, Colorado, Hawaii, Idaho, Michigan, Missouri, Montana, New Jersey, Ohio, Pennsylvania, and Washington) determine congressional redistricting by an independent or bipartisan redistricting commission. Five states: Maine, New York, Rhode Island, Vermont, and Virginia give independent bodies authority to propose redistricting plans, but preserve the role of legislatures to approve them. Arkansas has a commission composed of its governor, attorney general, and secretary of state. By law, the forty four states with more than one representative must redistrict after each decennial census to account for population shifts within the state as well as (when necessary) to add or remove congressional districts. Federal law (including the Constitution) does not prevent states from redistricting at any time between censuses, up to and including redistricting prior to each congressional election, provided such redistricting conforms to various federal laws. However, "mid decade" redistricting proposals (such as what occurred in 2003 in Texas) have typically been highly controversial. Because of this, many states prohibit mid decade redistricting, although this is more prevalent for state legislative redistricting than for congressional redistricting. Some also link it to a specific year or to the decennial census. It is unclear to what extent mid decade redistricting would be legal in those states. Apart from mid decade redistricting initiated by state legislatures (as happened in Texas), both federal and state courts can also order the redistricting of maps between censuses (because maps were ruled unconstitutional or against federal law, for example). Examples of this are the redistricting that occurred between the 2016 and 2018 elections in Pennsylvania or the redistricting that occurred in North Carolina.

State constitutions and laws also mandate which body has responsibility over drawing the state legislature boundaries. In addition, those municipal governments that are elected on a district basis (as opposed to an at large basis) also redistrict.

Gerrymandering, the practice of drawing district boundaries to achieve political advantage for legislators, involves the manipulation of district boundaries to leave out, or include, specific populations in a particular district to ensure a legislator's reelection or to advantage their party. In states where the legislature (or another body where a partisan majority is possible) is in charge of redistricting, the possibility of gerrymandering (the deliberate manipulation of political boundaries for electoral advantage, usually of incumbents or a specific political party) often makes the process very politically contentious, especially when the majorities of the two houses of the legislature, or the legislature and the governor, are from different parties. Partisan domination of state legislatures and improved technology to design contiguous districts that pack opponents into as few districts as possible have led to district maps which are skewed towards one party. Consequently, many states including Florida, Georgia, Maryland, Michigan, North Carolina, Ohio, Pennsylvania, Texas and Wisconsin have succeeded in reducing or effectively eliminating competition for most House seats in those states. Some states, including New Jersey and New York, protect incumbents of both parties, reducing the number of competitive districts. The state and federal court systems are often involved in resolving disputes over congressional and legislative redistricting when gridlock prevents redistricting in a timely manner. In addition, those disadvantaged by a proposed redistricting plan may challenge it in state and federal courts. Justice Department approval (which is known as pre clearance) was formerly required under Section 5 of the Voting Rights Act of 1965 in certain states that have had a history of racial barriers to voting. The Supreme Court's ruling on the Pennsylvania redistricting effectively allows elected officials to select their constituents by eliminating most of the grounds for constituents to challenge district lines.

Colegrove v. Green (1946)
Baker v. Carr (1962) — federal courts may review redistricting of state legislative districts
Gray v. Sanders (1963) — 14th Amendment's equal protection clause requires “one person, one vote” standard
Wesberry v. Sanders (1964) — legislative districts for the U. S. House of Representatives must be composed, to the extent practicable, of equal numbers of eligible voters
Burns v. Richardson (1966)
Reynolds v. Sims (1964)
Gaffney v. Cummings (1973)
Karcher v. Daggett (1983)
Thornburg v. Gingles (1986)
Davis v. Bandemer (1986)
Growe v. Emison (1993)
Voinovich v. Quilter (1993)
Shaw v. Reno (1993)
Johnson v. DeGrandy (1994)
Miller v. Johnson (1995)
Bush v. Vera (1996)
Hunt v. Cromartie (1999)
Vieth v. Jubelirer (2004)
League of United Latin American Citizens v. Perry (2006)
Bartlett v. Strickland (2009)
Arizona State Legislature v. Arizona Independent Redistricting Commission (2015)
Gill v. Whitford (2018)
Benisek v. Lamone (2018 & 2019)
Rucho v. Common Cause (2019)
Allen v. Milligan (2023)
Alexander v. South Carolina State Conference of the NAACP (2023)