Mixed-member majoritarian representation in the context of "National Assembly of Hungary"

A mixed electoral system is one that uses different electoral systems to elect different seats in a legislature. Most often, this involves a First Past the Post combined with a proportional component. The results of the combination may be mixed-member proportional (MMP), where the overall results of the elections are proportional, or mixed-member majoritarian, in which case the overall results are semi-proportional, retaining disproportionalities from the majoritarian component. Systems that use multiple types of combinations are sometimes called supermixed.

Mixed-member systems also often combine local representation (most often single-member constituencies) with regional or national (multi-member constituencies) representation, having multiple tiers. This also means voters often elect different types of representatives who might have different types of constituencies. Some representatives may be elected by personal elections where voters vote for candidates, and some by list elections where voters vote for electoral lists of parties.

A mixed single vote (MSV) is a type of ballot in mixed-member electoral systems, where voters cast a single vote in an election, which is used both for electing a local candidate and as a vote for a party affiliated with that candidate according to the rules of the electoral system. Unlike most mixed proportional and mixed majoritarian systems (such as parallel voting) where voters cast two votes, split-ticket voting is not possible under MSV. This significantly reduces the possibility of manipulating compensatory mixed systems, at the price of reducing voter choice. An alternative based on the mixed single vote that still allows for indicating different preferences on different levels is the mixed ballot, which functions as a preferential (mixed) single vote.

With MSV, voters usually cast their single vote for a local candidate in a single-member district (SMD) and then all votes (or just the wasted votes, depending on the system) from this lower tier are added to distribute seats between upper tier candidates, typically national party lists. How proportional the outcome is depends on many factors including the vote transfer rules (which votes are recounted as party list votes), whether there is a seat linkage, and other parameters (e.g. the number of list seats) used in the system. MSV systems originate from Germany and variations are currently used in Bolivia, Lesotho and Hungary for local elections in larger municipalities.

The additional-member system (AMS) is a two-vote seat-linkage-based mixed electoral system used for elections to the Scottish Parliament in the United Kingdom, although not for Westminster elections, in which most representatives are elected in single-member districts (SMDs), and a fixed number of other "additional members" are elected from a closed list to make the seat distribution in the chamber more proportional to the votes cast for party lists. It is a form of mixed-member proportional representation and is distinct from using parallel voting for the list seats (also known as the supplementary-member system) in that the "additional member" seats are awarded to parties taking into account seats won in SMDs (referred to as compensation or top-up) – these are ignored under parallel voting, which is a non-compensatory method.

AMS is the name given to a particular system used in the United Kingdom that aims to provide proportional representation. However, in theory it can fail to be proportional. This is commonly caused by dis-proportional district results caused by seat overhang. The proportionality of AMS depends on having enough additional ("top-up") seats and on how votes are cast in a specific election. During its use in the United Kingdom, AMS produced results closer to mixed-member proportional rather than mixed-member majoritarian representation.