The Treaty of Westminster, concluded between the Lord Protector of the English Commonwealth, Oliver Cromwell, and the States General of the United Netherlands, was signed on 5/15 April 1654. The treaty ended the First Anglo-Dutch War (1652–1654). The treaty is otherwise notable because it is one of the first treaties implementing international arbitration as a method of conflict resolution in early modern times. A secret clause, obliging the States of Holland to enact the Act of Seclusion, played an important part in Dutch internal politics during the First Stadtholderless Period.

The States General of the Netherlands is the supreme bicameral legislature of the Netherlands consisting of the Senate and the House of Representatives. Both chambers meet at the Binnenhof in The Hague.