Two-round system

The two-round system (TRS or 2RS), sometimes called ballotage, top-two runoff, or two-round <a href="/facts/First-past-the-post_voting/RJ11du1H">plurality</a>, is a single-winner <a href="/facts/Electoral_system/e6zvx3Bo">electoral system</a> which aims to elect a member who has support of the majority of voters. The two-round system involves one or two rounds of <a href="/facts/First-past-the-post_voting/RJ11du1H">choose-one voting</a>, where the voter marks a single favorite candidate in each round. If no one has a majority of votes in the first round, the two candidates with the most votes in the first round move on to a second election (a second round of voting). The two-round system is in the family of <a href="/facts/Plurality_voting/n4mcp5VF">plurality voting</a> systems that also includes <a href="/facts/First-preference_plurality/IJbdarn4">single-round plurality</a> (FPP). Like <a href="/facts/Instant-runoff_voting/td1Q35Wg">instant-runoff (ranked-choice) voting</a> and first past the post, it elects one winner. 
The two-round system first emerged in <a href="/facts/France/CxIeIKM3">France</a> and has since become the most common single-winner <a href="/facts/Electoral_system/e6zvx3Bo">electoral system</a> worldwide. Despite this, runoff-based rules like the two-round system and RCV have faced criticism from <a href="/facts/Social_choice_theory/ztMqy1bM">social choice theorists</a> as a result of their susceptibility to <a href="/facts/Center_squeeze/8JRxIxP5">center squeeze</a> (a kind of <a href="/facts/Spoiler_effect/2FTdnzPo">spoiler effect</a> favoring extremists) and the <a href="/facts/No-show_paradox/racmDXYL">no-show paradox</a>. This has led to the rise of <a href="/facts/Electoral_reform/BI3v4yek">electoral reform</a> movements which seek to replace the two-round system with other systems like <a href="/facts/Rated_voting/X5basu5o">rated voting</a>, particularly in France. 
As well, TRS means voters sometimes have to gather to vote a second time, and sometimes the intervening period of time is rife with discord.
In the United States, the first round is often called a jungle or top-two primary. <a href="/facts/Georgia_(U.S._state)/KKnTDY6F">Georgia</a>, <a href="/facts/Louisiana/2GvfFcKE">Louisiana</a>, <a href="/facts/California/zLW2vdQJ">California</a>, and <a href="/facts/Washington_(state)/7tCrTFnN">Washington</a> use the two-round system for all non-presidential elections. <a href="/facts/Mississippi/7KwuWxxT">Mississippi</a> uses it for state offices. Most other states use a <a href="/facts/Partisan_primary/rTfSBXDc">partisan primary</a> system that is often described as behaving like a two-round system in practice, with primaries narrowing down the field to two frontrunners. (<a href="/facts/Alaska/LlDNr2uR">Alaska</a> and <a href="/facts/Maine/7ww4UY8B">Maine</a> use the <a href="/facts/Instant-runoff_voting/td1Q35Wg">Instant-runoff voting</a> system, the ranked-choice voting (RCV) system, which unlike TRS does not require multiple rounds of voting.)

Two-round system open-in-new

Two-round system