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Tetracameralism (Greek: tetra-, four + Latin: camera, chamber) is the practice of having four legislative or parliamentary chambers. It is contrasted to unicameralism and bicameralism, which are far more common, and tricameralism, which is rarely used in government. No state currently has a tetracameral system.
Medieval Scandinavian deliberative assemblies were traditionally tetracameral, with 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 tetracameral Diet of Finland until 1906, when it was replaced by the unicameral Parliament.