A duumvirate is an alliance between two equally powerful political or military leaders. The term can also be used to describe a state with two different military leaders who both declare themselves to be the sole leader of the state.
It has been suggested that Vladimir Putin and Dmitry Medvedev represent a modern Russian duumvirate, sometimes referred as тандемократия, "tandemocracy", a portmanteau of "tandem" and "democracy". When they agreed to swap jobs in November 2011, with Putin retaking his old position of president which Medvedev had held for four years (because Putin was constitutionally barred from having a third term in a row), many in Russia called this "castling" ("рокировка" - "rokirovka") — after the move in chess when the king and a rook, a castle-shaped piece, swap sides. This "castling" was followed by protests, seen by some as "tandem malaise" - a feeling amongst sections of the population that they were fed up with the tandem. For most of Medvedev's presidency, Putin and he were seen as being roughly equal, but with the "castling" it became clear that Putin had the upper hand the whole time.
Andorra is nominally a duumvirate, as it is ruled by two ex officio co-princes, one of whom is François Hollande, the President of France, the other of whom is Joan Enric Vives i Sicília, Bishop of the Diocese of Urgell, although the Andorran prime minister wields de facto power as the head of government. Duumvirates in history include the city-states of Carthage, ruled by two mayors (Suffets), Ancient Rome, ruled by two Consuls, and Sparta, ruled by two kings.
Some political parties have duumvirates, sometimes, such as was the case of Russel Norman and Metiria Turei leading the Green Party of Aotearoa New Zealand.
The First Whitlam Ministry in Australia is sometimes called the "Duumvirate" because it consisted entirely of the Prime Minister, Gough Whitlam, and his deputy, Lance Barnard, who between them split up all ministerial and quasi-ministerial positions for two weeks in December 1972.
Sukarno and Mohammad Hatta in Indonesia were nicknamed the Duumvirate (Dwitunggal). As Vice President, Hatta quickly established himself as the day-to-day administrator of the government, with Sukarno setting government policy and then trying to win support for it.
- The port city of Umbar in the works of J.R.R. Tolkien was ruled by a duumvirate.
- In Pair of Kings the crown of Kinkow fell on twin brothers whose order of birth was never clearly accounted for; thus they reign as a duumvirate.
- Diarchy - rule by two people
- Duoviri - ancient Roman magistracy of two men
- Triumvirate - the equivalent term for three people
- Decemvirate - the equivalent term for ten people
- Coregency - rule by two regents
- Bailey, Nathan (1724). An universal etymological English dictionary. p. 269.
- Martin, Brian Joseph (2009), Beyond Weimar-Russia: The Putin-Medvedev Duumvirate as Imperial Revanchist (PDF), The Ohio State University
- Hale, Henry E.; Timothy J. Colton (8 September 2009). "Russians and the Putin-Medvedev "Tandemocracy": A Survey-Based Portrait of the 2007-08 Election Season" (PDF). The National Council for Eurasian and East European Research (Seattle, WA: University of Washington). Retrieved 15 March 2012.
- "Russian politics: is Kudrin the cure for Putin’s ‘tandem malaise’?". Open Democracy. Retrieved May 6, 2012.