The national assembly is a form of legislature that is used in the political systems of many different countries, either directly as a legislature or as the lower house of a bicameral legislature. The most famous national assembly is associated with France, where the first national assembly was established during the French Revolution in 1789. Because of its introduction during the French revolution, the concepts associated with national assembly are often associated with Francophone nations, although different forms of national assembly have spread all over the world and are also found in a number of Commonwealth countries.

In a historical context, a national assembly was often formed when an old order had dissolved due to decay, war, or revolution. This was the case in the French revolution, when members of the States General proclaimed the first ever national assembly in 1789. Two other examples of well known national assemblies around the world are the Federal Constitutional Convention of 1787 and the Frankfurt Parliament of 1848 to 1849. However, the name National Assembly is now applied to a number of chief legislative bodies around the world, both in Europe and beyond.

The different forms of government around the world make it difficult to define the concept of a national assembly, as each nation has unique national legislatures. Some countries have unicameral national legislatures, while other nations have their own versions of a bicameral legislature. Bicameral legislature have both an upper and a lower house, while alternate constitutional conventions and assemblies are defined by some nations as a particular version of a national assembly. While every country is different in terms of government, the defining principles of a national assembly are implicated in the structures of government in a large number of countries around the world.