The Acts of Union were two Parliamentary Acts - the Union with Scotland Act passed in 1706 by the Parliament of England, and the Union with England Act passed in 1707 by the Parliament of Scotland - which put into effect the terms of the Treaty of Union that had been agreed on 22 July 1706, following negotiation between commissioners representing the parliaments of the two countries. The Acts joined the Kingdom of England and the Kingdom of Scotland (previously separate states, with separate legislatures but with the same monarch) into a single, united kingdom named "Great Britain".
The two countries had shared a monarch since the Union of the Crowns in 1603, when King James VI of Scotland inherited the English throne from his double first cousin twice removed, Queen Elizabeth I. Although described as a Union of Crowns, until 1707 there were in fact two separate Crowns resting on the same head (as opposed to the implied creation of a single Crown and a single Kingdom, exemplified by the later Kingdom of Great Britain). There had been three attempts in 1606, 1667, and 1689 to unite the two countries by Acts of Parliament, but it was not until the early 18th century that both political establishments came to support the idea, albeit for different reasons.