Detail of William and Mary from the ceiling of the Painted Hall
The phrase William and Mary usually refers to the coregency over the Kingdoms of England, Scotland and Ireland, of spouses (and first-cousins) King William III & II and Queen Mary II. Their joint reign began in February 1689 after they were offered the throne by the Parliament of England following William's successful invasion of England in 1688, the so-called Glorious Revolution. They replaced James II & VII, Mary's father and William's uncle/father-in-law, who was "deemed to have fled" the country. Parliament offered William and Mary co-regency at the couple's behest. After Mary died in 1694, William ruled alone until his death in 1702. William and Mary were childless and were ultimately succeeded by Mary's younger sister, Anne.
To end the Glorious Revolution, William and Mary signed the English Bill of Rights and began a new co-operation between the Parliament and the monarchs, leading to a greater measure of personal liberty and democracy in Britain. This action both signaled the end of several centuries of tension and conflict between the crown and parliament, and the end of the idea that England would be restored to Roman Catholicism, King William being a Protestant leader. The English Bill of Rights also inspired the English colonists in North America to revolt against the rule of James II and his proposed changes in colonial governance. These colonial revolts occurred in Massachusetts, New York, and Maryland.
Stamp duty was first introduced in England during their reign with the act of 1694 titled "An act for granting to their Majesties several duties upon vellum, parchment and paper, for four years, towards carrying on the war against France".
Their names were lent to the second institution of higher learning in the United States, The College of William and Mary, which was founded in 1693 under a royal charter.