A bicameral legislature divides the legislators into two separate assemblies, chambers, or houses. Bicameralism is distinguished from unicameralism, in which all members deliberate and vote as a single group, and from some legislatures that have three or more separate assemblies, chambers, or houses.

Often, the members of the two chambers are elected or selected by different methods, which vary from country to country. This can often lead to the two chambers having very different compositions of members.

Enactment of primary legislation often requires a concurrent majority – the approval of a majority of members in each of the chambers of the legislature. When this is the case, the legislature may be called an example of perfect bicameralism. However, in many Westminster system parliaments, the house to which the executive is responsible can overrule the other house and may be regarded as an example of imperfect bicameralism. Some legislatures lie in between these two positions, with one house only able to overrule the other under certain circumstances.