Condominium (international law)

A condominium (plural either "condominia", as in Latin, or condominiums) in international law is a political territory (state or border area) in or over which multiple sovereign powers formally agree to share equal "dominium" (in the sense of sovereignty) and exercise their rights jointly, without dividing it into "national" zones.
Although a condominium has always been recognized as a theoretical possibility, condominia have been rare in practice. A major problem, and the reason so few have existed, is the difficulty of ensuring co-operation between the sovereign powers; once the understanding fails, the status is likely to become untenable.
The word is recorded in English since c. 1714, from Modern Latin, apparently coined in Germany c. 1700 from Latin "com-" "together" + "dominium" "right of ownership" (compare domain). A condominium of three sovereign powers is sometimes called a tripartite condominium or tridominium.
Current condominia.
Abyei Area.
The 2005 Comprehensive Peace Agreement that ended the Second Sudanese Civil War, created a special status administrative area known as the Abyei Area, which is considered to simultaneously be part of West Kordofan state and Northern Bahr el Ghazal state. Following the independence of South Sudan in 2011, the area effectively became a condominium between the Republic of South Sudan and the Republic of the Sudan.
Antarctica.
Antarctica is a "de facto" continental condominium, governed by the 29 parties to the Antarctic Treaty that have consulting status.
Brčko District.
In Bosnia and Herzegovina, the Brčko District forms a condominium between the Federation of Bosnia and Herzegovina and Republika Srpska.
Gulf of Fonseca.
El Salvador, Honduras, and Nicaragua exercise a tripartite condominium over parts of the Gulf of Fonseca and of the territorial sea outside its mouth.
Joint Regime Area.
Colombia and Jamaica share a maritime condominium (called a "Joint Regime Area") in the Caribbean Sea by mutual agreement as an alternative to delimiting their sea boundary. The outer portion of the EEZ of each country otherwise would overlap in this area. Unlike other "joint development zones", this condominium appears not to have been purposed simply as a way to divide oil, fisheries or other resources.
Lake Constance.
Austria, Germany, and Switzerland consider themselves to hold a tripartite condominium (albeit on different grounds) over the main part of Lake Constance (without its islands). On the other hand, Switzerland holds the view that the border runs through the middle of the lake. Hence, no international treaty establishes where the borders of Switzerland, Germany, and Austria, in or around Lake Constance, lie.
Moselle.
The Moselle and its tributaries, the Sauer and the Our, constitute a condominium between Germany and Luxembourg, which also includes bridges, about 15 river islands of varying size, and the tip of one island, "Staustufe Apach", near Schengen (the rest of the island is in France). The condominium was established by treaty in 1816.
Pheasant Island.
Pheasant Island (also known as Conference Island, "Konpantzia" in Basque, "Île de la Conférence" in French or "Isla de los Faisanes" in Spanish) in the Bidassoa is a condominium between France and Spain. It was established by the Treaty of the Pyrenees in 1659. It is formally controlled by Spain between 1 February and 31 July each year and by France for the following six months. The island has no permanent population and has been eroded significantly by the river.
Co-principality.
Under French law, Andorra was once considered to be a French–Spanish condominium, although it is more commonly classed as a co-principality, since it is itself a sovereign state, not a possession of one or more foreign powers. However, the position of head of state is shared "ex officio" by two foreigners, one of whom is the President of France, currently Emmanuel Macron, and the other the Bishop of Urgell in Spain, Joan Enric Vives i Sicília.