Republicanism is the ideology of governing a nation as a republic, where the head of state is appointed by means other than heredity, often elections. The exact meaning of republicanism varies depending on the cultural and historical context. Several definitions are covered in this article.

Some political scientists^[who?] use the term 'republic' to indicate rule by many people and by law, as opposed to monarchy, or arbitrary rule by one person. By this definition, dictatorial states are not republics while, according to some such as Kant, constitutional monarchies may be. Kant also supports Republicanism over pure democracy on the grounds that the latter is the unrestricted rule of the majority unrestrained by law.

In Ancient Greece several philosophers and historians set themselves to analysing and describing forms of government of classical republicanism. Some scholars have translated the Greek concept of "politeia" as "republic," but most modern scholars reject this idea.There is no single written expression or definition from this era that exactly corresponds with a modern understanding of the term "republic." However, most of the essential features of the modern definition are present in the works of Plato, Aristotle, Polybius, and other ancient Greeks. These elements include the ideas of mixed government and of civic virtue. It should be noted that the modern title of Plato's dialogue on the ideal state (The Republic) is a misnomer when seen through the eyes of modern political science (see Republic (Plato)).