A personal union is a relationship of two or more entities that are considered separate, sovereign states, which, through established law, share the same person as their respective head of state. It is not to be confused with a federation, which internationally is considered as a single state.

Personal unions can arise for very different reasons, ranging from near coincidence (a princess who is already married to a king becomes pregnant, and their child inherits the crown of both countries) to virtual annexation (where a personal union sometimes was seen as a means of preventing uprisings). They can also be codified (the constitutions of the states clearly express that they shall share the same person as head of state), or non-codified (in which case they can easily be broken by e.g. different succession rules).

Because presidents of republics are ordinarily chosen from within the citizens of the state in question, personal unions are almost entirely a phenomenon of monarchies, and sometimes the term dual monarchy is used to signify a personal union between two monarchies. With the decline of monarchies during the 20th century, personal unions have become quite uncommon. Where they do exist is most notably between the Commonwealth Realms, where, beyond the United Kingdom, the Governor-General is the vice-regal representative of the Monarch.

There is a somewhat grey area between personal unions and federations, and the first has regularly grown into the second. This article is an attempt at listing some historical and contemporary personal unions.

Kingdom of England (927 - 1707)

Norway from 1013 to 1014 and again from 1028 to 1035

Denmark from 1013 to 1014, from 1016 to 1035 and again from 1040 to 1042

Normandy from 1066 to 1087 and again from 1106 to 1204/1259

Anjou from 1153 to 1204

Aquitaine from 1153 to 1362, from 1377 to 1390, and again from 1399 to 1449

Lordship of Ireland from 1171 to 1541

Principality of Wales from 1282 to 1535-1542 (when Wales and England were united in the Acts of Union)

Kingdom of Ireland from 1541 to 1707

Scotland from 1603 to 1707 (when they were joined together in the Kingdom of Great Britain)

Netherlands from 1689 to 1702, with the Stadtholder of the Netherlands also serving as King of England, Scotland and Ireland. Only two Dutch provinces never entered into the personal union: Friesland and Groningen.

Kingdom of Scotland (843 - 1707)

Personal union with England and Ireland from 1603 to 1707 (when England and Scotland were joined together in the Kingdom of Great Britain)

Personal union with the Netherlands from 1689 to 1702, with the Stadtholder of most of the provinces of the Netherlands also serving as King of Scotland, England and Ireland. The actual situation was slightly more complex with the Dutch provinces Holland, Zeeland and Utrecht entering into personal union in 1672, Guelders and Overijssel in 1675 and Drenthe in 1696. Only 2 Dutch provinces never entered into the personal union: Friesland and Groningen.

Kingdom of Great Britain (1707 - 1801)

Ireland from 1707 to 1801 (when they were joined together in the United Kingdom of Great Britain and Ireland)

Hanover from 1714 to 1801

Corsica from 1794 to 1796

United Kingdom of Great Britain and Ireland (1801 - 1927)

Hanover from 1801 to 1837

United Kingdom of Great Britain and Northern Ireland (1927 - present)

Former

Ireland - 1927 to 1949

India - 1947 to 1950

Union of South Africa - 1931 to 1961

Pakistan - 1947 to 1956

Ceylon now Sri Lanka - 1948 to 1972

Ghana - 1957 to 1960

Sierra Leone - 1961 to 1971

Nigeria - 1960 to 1963

Tanganyika now Tanzania - 1961 to 1962

Uganda - 1962 to 1963

Trinidad and Tobago - 1962 to 1976

Kenya - 1963 to 1964

Malawi - 1964 to 1966

Malta - 1964 to 1974

Gambia - 1965 to 1970

Guyana - 1966 to 1970

Mauritius - 1968 to 1992

Fiji - 1970 to 1987

Current

Canada, through the Statute of Westminster in 1931

Australia, through adoption of the Statute of Westminster in 1942 (retroactive to 1939)

New Zealand, through adoption of the Statute of Westminster in 1947

Jamaica, through independence in 1962

Barbados, through independence in 1966

The Bahamas, through independence in 1973

Grenada, through independence in 1974

Papua New Guinea, through independence in 1975

The Solomon Islands, through independence in 1978

Tuvalu, through independence in 1978

Saint Lucia, through independence in 1979

Saint Vincent and the Grenadines, through independence in 1979

Antigua and Barbuda, through independence in 1981

Belize, through independence in 1981

Saint Kitts and Nevis, through independence in 1983