Since its transition to democracy in the late 1970s, Spain has been organized in a quasi-federal system called the "State of Autonomies". Each Autonomous Community is required by the Constitution to have its own three-branched system of government with its basic rules codified in a special law called a Statute of Autonomy, a sort-of regional constitution. Although there is no Constitutional requirement imposed upon regional elections other than that they must be based in proportional methods, all regional legislatures are unicameral, their members being elected in multi-member constituencies matching the provinces in the Autonomous Community with seats allocated to party lists using the D'Hondt method.