The abolition of monarchy is a legislative or revolutionary movement to abolish monarchical elements in government, usually hereditary. The abolition of an absolute monarchy in favour of limited government under a constitutional monarchy is a less radical form of anti-monarchism that has succeeded in some nations that still retain monarchs, such as Sweden, Spain, and Thailand.

Abolition has been carried out in various ways, including via abdication leading to the extinction of the monarchy, legislative reform, revolution, coup d'état, and decolonisation. Abolition became more frequent in the 20th century, with the number of monarchies in Europe falling from 22 to 12 between 1914 and 2015, and the number of republics rising from 4 to 34. Decolonisation and independence have resulted in an abolition of monarchies in a number of former colonies such as those created by the United Kingdom.

Motivations for abolition include egalitarianism and anti-class views, eliminating a rival system potentially opposed to another incoming system (as had occurred in Romania in 1947), opposition to undemocratic and hereditary institutions, perception of monarchy as anachronistic or outdated, and opposition to a particular monarch or dynasty. In many colonies and former colonies, abolishing the influence of the monarchy of a colonising state is considered part of decolonisation. In many Commonwealth realms, the monarchy may be viewed as a foreign institution running counter to the national identity or national sovereignty.

In the 21st century, some countries that are monarchies have significant republican movements, such as Spain and Australia. Since the beginning of the 20th century, restorations of monarchies have been comparatively rare. Examples are the monarchy of Spain, which since 1947 had been nominally a regency with a vacant throne but the Bourbon dynasty was restored in 1975; the reinstatement in 1991 of the Emir of Kuwait following abolition in 1990 and the Gulf War; and a 1993 transition of Cambodia from a Marxist-Leninist republic to an elective monarchy.

The city-state of Athens was ruled by monarchs in a period before the establishment of Athenian Democracy. Most of this is either mythical or semi-historical. The Athenian monarchy was abolished and replaced with lifetime archons around 1068 BC, whose power was reduced over many years.

The Roman Republic was established after the overthrow of the seventh king of Rome, Lucius Tarquinius Superbus, in 509 BC, after his disrespect for Roman customs and the Senate as well as his use of violence to control Rome.

Under the leadership of Oliver Cromwell, in 1649, King Charles I was tried for high treason, convicted and executed. This marked the conclusion of the English Civil War which resulted in the Parliament of England overthrowing the English monarchy, and initiating a period of an English republic (known as the Wars of the Three Kingdoms). After eleven years, in 1660, a limited monarchy was restored but moderated by an independent Parliament.

In the Kingdom of England, the Glorious Revolution of 1688 furthered the constitutional monarchy, restricted by laws such as the Bill of Rights 1689 and the Act of Settlement 1701. At the same time, in Scotland, the Convention of Estates enacted the Claim of Right Act 1689, which placed similar limits on the Scottish monarchy.