• Laws in Wales Acts 1535–1542, passed by the Parliament of England, annexing Wales to England, sometimes known as the "Acts of Union"

• Tender of Union, (Act of Union 1652‎), annexation of Scotland by the Commonwealth of England

• Acts of Union 1707, passed by both the Parliament of England and the Parliament of Scotland to form the Kingdom of Great Britain

• Act of Union 1800, passed by both the Parliament of Great Britain and the Parliament of Ireland to form the United Kingdom of Great Britain and Ireland

• Act of Union 1840, passed by the Parliament of the United Kingdom, joining Upper Canada and Lower Canada (to form the Province of Canada)

• South Africa Act 1909, passed by the Parliament of the United Kingdom creating the Union of South Africa, is sometimes referred to as the Act of Union

• Act of Union 1814 forming a personal union between Sweden and Norway

• Danish-Icelandic Act of Union 1918 granted independence to Iceland

Other meanings

• The poem by Seamus Heaney, written in 1975.