The British Royal Family is the group of close relatives of the monarch of the United Kingdom. The term is also commonly applied to the same group of people who are the relations of the monarch in her or his role as sovereign of any of the other Commonwealth realms, thus sometimes at variance with official national terms for the family. Members of the Royal Family belong to, either by birth or marriage, the House of Windsor, since 1917, when George V changed the name of the royal house from Saxe-Coburg and Gotha. This decision was primarily taken because Britain and her Empire were at war with Germany and given the British Royal Family's strong German ancestry; it was felt that its public image could be improved by choosing a more British house name. The new name chosen, Windsor, had absolutely no connection other than as the name of the castle which was and continues to be a royal residence.

Although in the United Kingdom there is no strict legal or formal definition of who is or is not a member of the Royal Family, and different lists will include different people, those carrying the style Her or His Majesty (HM), or Her or His Royal Highness (HRH) are always considered members, which usually results in the application of the term to the monarch, the consort of the monarch, the widowed consorts of previous monarchs, the children of the monarch and previous monarchs, the male-line grandchildren of the monarch and previous monarchs, and the spouses and the widows of a monarch's and previous monarch's sons and male-line grandsons. On 30 November 1917, King George V issued Letters Patent defining who are members of the Royal Family; the text of the notice from the London Gazette is as follows:

In 1996, Her Majesty The Queen modified these Letters Patent, as was evidenced by this Notice from the London Gazette:

In 2013 Letters Patent were issued to extend a title and a style borne by members of the Royal Family to additional persons to be born, evidenced by this Notice from the London Gazette:

Members and relatives of the British Royal Family historically represented the monarch in various places throughout the British Empire, sometimes for extended periods as viceroys, or for specific ceremonies or events. Today, they often perform ceremonial and social duties throughout the United Kingdom and abroad on behalf of the United Kingdom. Aside from the monarch, their only constitutional role in the affairs of government is to serve, if eligible and when appointed by letters patent, as a Counsellor of State, two or more of whom exercise the authority of the Crown (within stipulated limits) in the indisposal or absence from the British realm of the monarch. In the other realms of the Commonwealth royalty do not serve as Counsellors of State. However in each such realm the monarch's family members may act on behalf of, are funded by, and represent the sovereign of that particular state, and not the United Kingdom.

The Queen, her consort, her children and grandchildren, as well as all former sovereigns' children and grandchildren hold places in the first sections of the official orders of precedence in England and Wales, Scotland, and Northern Ireland. Wives of the said enjoy their husbands' precedence, and husbands of princesses are unofficially but habitually placed with their wives as well. However, the Queen changed the private order of precedence in the Royal Family in favour of Princesses Anne and Alexandra, who henceforth take private precedence over the Duchess of Cornwall, who is otherwise the realm's highest ranking woman after the Queen herself. She did not alter the relative precedence of other born-princesses, such as the daughters of her younger sons.