(CNN) This year, Maine will be the first state to use ranked choice voting in a federal election. This applies to the presidential race, as well as the US House and US Senate.
Here's what to know about the system.
It lets voters literally rank their choices in order of preference, marking candidates as their first, second and third choice picks (and so on).
The winner must have a majority (more than 50% of the votes) rather than a plurality (simply the most votes).
In Maine, ranked choice only takes effect when three or more candidates are on the ballot. Voting is counted by round, with lowest-ranked candidates eliminated in each round until only two candidates remain.
On election night, if there is no clear winner with more than 50% of the vote, counting goes into ranked choice voting tabulation rounds. In Maine, couriers are sent around the state to either collect actual ballots or memory devices and brought to a secure location at the State Capitol in Augusta. There, high speed tabulators count the results and determine the winner.
"The process takes about a week, a week and a half," Kristen Muszynski, communications director for Maine's secretary of state, told CNN.
No. A voter only needs to mark a first choice, or as many as they want.
But a voter can only put one candidate first, or second and so on. In Maine, If you choose two candidates for your first choice, it counts as an over vote and your vote will not count, "since your intent for your first choice cannot be determined."
Advocates say it helps prevent spoiler candidates -- and ensures the candidate with the most support wins, rather than one who emerges from a crowded field with a small plurality of votes.
It can be especially helpful in crowded primaries or elections where margins of victory are very small, ensuring the candidate has the support of the majority, rather than a small plurality.
At least 18 municipalities across the country, including mayor and city council elections in Minneapolis and St. Paul, Minnesota and the mayor, city council and city auditor elections in Berkeley, California, according to a tally by FairVote.org, a group advocating for ranked choice voting in the US.
New York City is poised to use it in all city primary and special elections starting in 2021.
Two California governors have vetoed measures that would have given cities and towns across the state the option of using ranked choice voting. It was already in use by San Francisco, Oakland, Berkeley and San Leandro.
Gov. Jerry Brown vetoed the bill in 2016, calling it "overly complicated and confusing. I believe it deprives voters of genuinely informed choice."
In 2019, Gov. Gavin Newsom issued another veto for a measure that would have allowed ranked choice voting to be used in local elections, echoing the concern that it adds to voter confusion. "The state would benefit from learning more from charter cities who use ranked choice voting before broadly expanding the system," Newsom wrote in the veto message.
It is on the statewide ballot in Massachusetts this fall. If voters approve it -- and barring legal challenge -- it would take effect in 2022 for primary and general elections for all Massachusetts statewide offices, state legislative offices, federal congressional offices and certain other offices.
It would not apply to elections for president, county commissioner or regional district school committee member.
The city of Cambridge, Massachusetts, has used it to elect its city councilors and school committee members since the 1940s. Cambridge resident (and Massachusetts Senator) Elizabeth Warren recently backed Massachusetts' effort in an op-ed with Maryland Rep. Jamie Raskin. Takoma Park, which is in Raskin's congressional district, has used ranked choice voting since 2007 for all mayor and city council elections.
"By requiring the winner to reach more than 50 percent of the vote, ranked-choice voting ensures the winning candidate is the one with the broadest appeal to the majority of voters," Warren and Raskin wrote. "The ability to mobilize the broadest and deepest appeal across the electorate would replace the ability to target a passionate minority constituency, which may be extreme or nonrepresentative from the standpoint of most voters as the key to winning."
CORRECTION: This story has been updated to accurately describe ranked-choice legislation that was vetoed in California.