The Act of Union is a name given to several acts passed by the English, Scottish and British parliaments from 1536 onwards. Among those:

• Act of Union 1536 joining England and Wales (as England)
• Act of Union 1707 joining Scotland and England (to form Great Britain)
• Act of Union 1800 joining Ireland to Great Britain (to form the United Kingdom)
• Act of Union 1840 joining Upper Canada and Lower Canada (to form the Province of Canada).

The term "act of union" is also used as a euphemism for sexual intercourse.

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