Act of Union may refer to:

• Laws in Wales Acts 1535 and 1542, passed during the reign of King Henry VIII to make Wales a part of the Kingdom of England, often referred to in the plural as the "Acts of Union" (Welsh, Y Deddfau Uno)
• Tender of Union (Act of Union 1652), Tender of Union uniting Scotland with 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
• Acts 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 UK, joining Upper Canada and Lower Canada to form the Province of Canada
• South Africa Act 1909, passed by the Parliament of the UK creating the Union of South Africa, sometimes referred to as the Act of Union

• Riksakten (Act of Union 1814), the Union between Sweden and Norway, forming a personal union between Sweden and Norway
• Danish–Icelandic Act of Union, a 1918 union granting independence to Iceland

• Act of Union, a poem by Seamus Heaney, written in 1975
• Bull of Union with the Greeks (Laetentur Caeli), a 1439 papal bull sometimes referred to as the Act of Union

This disambiguation page lists articles associated with the title Act of Union.
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