A bicameral legislature is one in which the legislators are divided into two separate assemblies, chambers or houses. Bicameralism is distinguished from unicameralism, in which all of the members deliberate and vote as a single group, and from some legislatures which have three or more separate assemblies, chambers or houses.Most legislatures are bicameral. Often, the members of the two chambers are elected or selected using different methods, which vary from country to country. Enactment of primary legislation often requires a concurrent majority, the approval of a majority of members in each of the chambers of the legislature. However, in many Westminster system parliaments, the house to which the executive is responsible can overrule the other house.Bicameralism is an essential and defining feature of the classical notion of mixed government.