Various electoral systems are now used in Scotland. Historically, First Past the Post had been used in most types of elections, but pressure for change has gradually seen the introduction of different systems, especially towards the end of the 20th century and the beginning of the 21st. This history of using First Past the Post means that the development of political parties in Scotland was affected to some extent by Duverger's Law

Duverger's law

In political science, Duverger's law is a principle which asserts that a plurality rule election system tends to favor a two-party system. This is one of two hypotheses proposed by Duverger, the second stating that “the double ballot majority system and proportional representation tend to...

, which causes the agglomeration of related political ideologies into a few large parties with many small parties rarely winning representation, though a four party system did develop in Scotland prior to the introduction of voting reform.

Electoral systems now used in Scotland are:

• The First Past the Post system is used for UK general elections
  United Kingdom general elections
  This is a list of United Kingdom general elections since the first in 1802. The members of the 1801–1802 Parliament had been elected to the former Parliament of Great Britain and Parliament of Ireland, before being co-opted to serve in the first Parliament of the United Kingdom, so that Parliament...
  
  .
• The Additional Member System
  Mixed member proportional representation
  Mixed-member proportional representation, also termed mixed-member proportional voting and commonly abbreviated to MMP, is a voting system originally used to elect representatives to the German Bundestag, and nowadays adopted by numerous legislatures around the world...
  
   is used for elections to the Scottish Parliament
  Scottish Parliament
  The Scottish Parliament is the devolved national, unicameral legislature of Scotland, located in the Holyrood area of the capital, Edinburgh. The Parliament, informally referred to as "Holyrood", is a democratically elected body comprising 129 members known as Members of the Scottish Parliament...
  
  .
• The Single Transferable Vote
  Single transferable vote
  The single transferable vote is a voting system designed to achieve proportional representation through preferential voting. Under STV, an elector's vote is initially allocated to his or her most preferred candidate, and then, after candidates have been either elected or eliminated, any surplus or...
  
   system is used to elect local councils.
• The Party List System
  Party-list proportional representation
  Party-list proportional representation systems are a family of voting systems emphasizing proportional representation in elections in which multiple candidates are elected...
  
   is used for European Parliament
  European Parliament
  The European Parliament is the directly elected parliamentary institution of the European Union . Together with the Council of the European Union and the Commission, it exercises the legislative function of the EU and it has been described as one of the most powerful legislatures in the world...
  
  elections.