In contrast to unicameralism, and bicameralism, multicameralism is the condition in which a legislature is divided into more than two deliberative assemblies, which are commonly called "chambers" or "houses". This usually includes tricameralism with three chambers, but can also describe a system with any amount more. The word "multicameral" can also relate in other ways to its literal meaning of "many chambered" with use in science or biology.
Approximately half of the world's sovereign states are unicameral, and newer democracies and more recent constitutions are more often unicameral than not. More specifically many countries have switched to unicameralism whereas the opposite is rare. Nevertheless, many current parliaments and congresses still have a multicameral (usually bicameral) structure, which some claim provides multiple perspectives and a form of separation of powers within the legislature.
The principal advantage of a unicameral system is more democratic and efficient lawmaking, as the legislative process is simpler and there is no possibility of deadlock between two chambers. Proponents of unicameralism have also argued that it reduces costs, even if the number of legislators stay the same, since there are fewer institutions to maintain and support it financially. Proponents of bicameral legislatures allege that this offers the opportunity to re-debate and correct errors in either chamber in parallel, and in some cases to introduce legislation in either chamber.
At higher degrees of multicameralism, Medieval Scandinavian deliberative assemblies traditionally had four estates: the nobility, the clergy, the burghers, and the peasants. The Swedish and Finnish Riksdag of the Estates maintained this tradition the longest, having four separate legislative bodies. Finland, as a part of Imperial Russia, used the four-chambered Diet of Finland until 1906, when it was replaced by the unicameral Parliament.
The Federal Assembly of Yugoslavia originally had five chambers. After Yugoslavia adopted a new constitution in 1963, its legislature was restructured into four chambers each representing the various sectors of Yugoslav society with an additional chamber representing the general population. The Federal Assembly was the only legislature anywhere with five chambers, and a constitutional amendment added a sixth component described as either a chamber or sub-chamber. Yugoslavia adopted yet another constitution in 1974, abolishing the Federal Assembly and replacing it with a bicameral legislature.
Multicameralism remained commonplace within Europe until approximately 1800, after which most European governments gradually became bicameral, partly as a consequence of reforms associated with the French Revolution, but also as a consequence of new constitutional theories and subsequent pressures for constitutional reformCS1 maint: others (link)
The real patterns of the past are those that disappeared because they were abolished more or less recently. Most of them can be jointly defined as 'multicameralism', because they featured a number of chambers greater than two.
The council of nations, which was a to reflect a pluralistic ethnic structure and to assure equality among federal units and ethnic communities in the federal parliament, was still a 'sub-chamber' of the federal chamber in the five-chamber federal assembly. Its competences were very limitedCS1 maint: others (link)
Ten years later, the Constitution of 1963 completely changed the whole structure of the Federal Assembly and of all the other organs of State authority. It introduced a heavy and complicated system of five or, in some cases, even six "Councils", for which the term "Chamber" seems more appropriate in order to avoid confusion between these bodies and various other councils.