Editing By-election (section)

== In single-member constituencies ==

[[File:The Brentford Election (BM Y,4.574).jpg|thumb|A 1768 political cartoon about a by-election during the [[Middlesex election affair]].]]

By-elections are held in most nations that elect their parliaments through [[single-member constituencies]], whether [[Two-round system|with]] or [[First-past-the-post voting|without]] a [[Two-round system|runoff]] round. This includes most [[Commonwealth of Nations|Commonwealth]] countries, such as the [[United Kingdom]], [[Canada]], [[Australia]] and [[New Zealand]], as well as non-Commonwealth countries such as [[France]] and [[Italy]] (until 2006).<ref>{{cite book |language=it |url=https://www.academia.edu/2420626 |first=Giampiero |last=Buonomo |title=I subentri nelle assemblee parlamentari |publisher=Quaderni costituzionali |date=2006}}</ref> However, in some cases, such as the [[French National Assembly]], by-elections are only used to fill some vacancies, with the others being filled by the assumption of a seat by a [[running mate]] nominated by the vacator.{{cn|date=November 2024}}

In the United States, these contests have been called "special elections" because they do not always occur on [[Election Day (United States)|Election Day]] like regular congressional elections. Special elections are held when a seat in the [[United States House of Representatives|House of Representatives]], [[State legislature (United States)|state legislature]], or [[Local government in the United States|local legislature]] becomes vacant. At the federal level, the [[Article One of the United States Constitution#Clause 4: Vacancies|U.S. Constitution]] requires that vacancies in the House of Representatives be filled with a special election<ref>{{cite constitution|article=1|clause=4|section=2|polity=United States|date=1789}}</ref> (unlike the [[US Senate|Senate]], where it is up to law of the state involved to determine how the vacancy is filled).<ref>{{cite constitution|amendment=17|section=2|polity=United States|ratified=1913}}</ref> In most cases where a vacancy is filled through a special election, a primary will also be held to determine which candidates will represent the major parties.