A reign is the period of a person's or dynasty's occupation of the office of monarch of a nation (e.g., Saudi Arabia, Belgium, Andorra), of a people (e.g., the Franks, the Zulus) or of a spiritual community (e.g., Catholicism, Tibetan Buddhism, Nizari Ismailism).^[1] In most hereditary monarchies and some elective monarchies (e.g., Holy Roman Empire) there have been no limits on the duration of a sovereign's reign or incumbency, nor is there a term of office. Thus, a reign usually lasts until the monarch dies, unless the monarchy itself is abolished or the monarch abdicates or is deposed.

In elective monarchies, there may be a fixed period of time for the duration of the monarch's tenure in office (e.g., Malaysia).

The term of a reign can be indicated with the abbreviation "r." (for Latin rexit) after a sovereign's name,^[2] such as the following:

George VI, King of Great Britain, Ireland and the British Dominions, Emperor of India (r. 1936–1952)

Notable^{[clarification needed]} reigns have included the following.

• Queen Victoria of the United Kingdom of Great Britain and Ireland, Empress of India reigned from 1837 to 1901.
• King Victor Emmanuel III of Italy reigned from 1900 to 1946.
• King Bhumibol Adulyadej of Thailand reigned from 1946 to 2016.
• Queen Elizabeth II of the Commonwealth realms reigned from 1952 to 2022.
• Pope John XXIII reigned from 1958 to 1963.
• Emperor Akihito of Japan reigned from 1989 to 2019.

A reign can be ended in several ways:

• Abdication
• Abolition of monarchy
• Death
• Deposition

• Interregnum
• Rex (title)