In politics, a national assembly is either a unicameral legislature, the lower house of a bicameral legislature, or both houses of a bicameral legislature together. In the English language it generally means "an assembly composed of the representatives of the nation." The population base represented by this name is manifestly the nation as a whole, as opposed to a geographically select population, such as that represented by a provincial assembly. The powers of a National Assembly vary according to the type of government. It may possess all the powers of government, generally governing by committee, or it may function solely within the legislative branch of the government.

The name also must be distinguished from the concept. Conceptually such an institution may appear under variety of names, especially if "national assembly" is being used to translate foreign names of the same concept into English. Also, the degree to which the National Assembly speaks for the nation is a variable. To achieve a quorum, the ancient Athenian Assembly employed Scythian police to arrest citizens at random from the street. On the other hand, the early Parliaments of Europe were mainly of an aristocratic composition. The word had its origins and inspirations from the National Assembly that was responsible for drafting a constitution during the French Revolution.

The exact words, "national assembly," have been used prolifically in the international community of nations since the 18th and 19th centuries, considered the Age of Revolution in western Europe. Nations that formed republics in this age subsequently formed empires. Extensive cross-cultural influences brought much of their language and institutions to the provinces. When these empires collapsed finally, the emancipated countries formed states and other institutions on the model of the former imperial nations. Some examples of international influences are as follows:

In Germany, a Nationalversammlung was elected following the revolutions of 1848–1849 and 1918–1919, to be replaced by a permanent parliament (Reichstag) later. The legislature of the Estado Novo regime in Portugal was known as the National Assembly. The national assembly was also defined in the Republic of China constitution. This is different from the Legislative Yuan by the ROC constitution. In 2005, Taiwan revised the constitution and the national assembly was abolished. Examples have multiplied greatly under the policy of self-determination adopted by the western nations. Many more are to be found in the articles listed below.