Diarchy (or dyarchy) is a society or an organization with two rulers on an equal standing. Diarchies are known from ancient Sparta, Rome, Carthage as well as from Germanic (see Germanic king),India and Dacian tribes. Ranks in the Inca Empire were structured in moieties, with two occupants of each rank, but with different prestige, one hanan (upper) and one hurin (lower).

Examples of modern forms are the governments of Andorra and San Marino.

Examples of English rulers

• Hengest and Horsa
• Ethelred of Wessex and Alfred the Great
• William III and Mary II ruled jointly in England, Ireland and Scotland from 1689 to 1694

Examples of Diarchies

• India

Examples of Swedish kings

• Erik and Alrik
• Yngvi and Alf
• Björn at Hauge and Anund Uppsale
• Eric the Victorious and Olof (II) Björnsson
• Eric the Victorious and Olof Skötkonung
• Haakon the Red and Ingold I

Forms of government

Doppelherrschaft | Diarchie | 二頭政治 | Двоевластие | Diarki