Succession to the British throne is determined by descent, sex (for people born on or before 28 October 2011), legitimacy, and religion. Under common law, the Crown is inherited by a sovereign's children or by a childless sovereign's nearest collateral line. The Bill of Rights 1689 and the Act of Settlement 1701 restrict succession to the throne to the legitimate Protestant descendants of Sophia of Hanover who are in "communion with the Church of England". Spouses of Roman Catholics were disqualified from 1689 until the law was amended in 2015. Protestant descendants of those excluded for being Roman Catholics are eligible.
Queen Elizabeth II is the sovereign, and her heir apparent is her eldest son, Charles, Prince of Wales. Next in line after him is Prince William, Duke of Cambridge, the Prince of Wales's elder son. Third in line is Prince George, the eldest child of the Duke of Cambridge, followed by his sister, Princess Charlotte, and younger brother, Prince Louis. Sixth in line is Prince Harry, Duke of Sussex, the younger son of the Prince of Wales. Under the Perth Agreement, which came into effect in 2015, only the first six in line of succession require the sovereign's consent before they marry; without such consent, they and their children would be disqualified from succession.
The first four individuals in the line of succession who are over 21, and the sovereign's consort, may be appointed Counsellors of State. Counsellors of State perform some of the sovereign's duties in the United Kingdom while he or she is out of the country or temporarily incapacitated. Otherwise, individuals in the line of succession need not have specific legal or official roles.
The United Kingdom is one of the 16 Commonwealth realms. Each of those countries has the same person as monarch and the same order of succession. In 2011, the prime ministers of the realms agreed unanimously to adopt a common approach to amending the rules on the succession to their respective Crowns so that absolute primogeniture would apply for persons born after the date of the agreement, instead of male-preference primogeniture, and the ban on marriages to Roman Catholics would be lifted, but the monarch would still need to be in communion with the Church of England. After the necessary legislation had been enacted in accordance with each realm's constitution, the changes took effect on 26 March 2015.