Her husband, Prince Philip, the Duke of Edinburgh, died on 9 April 2021, aged 99. The prince married Princess Elizabeth in 1947, five years before she became Queen.
Find out more about the Royal Family and the line of succession below.
The Queen is the UK's longest-serving monarch, having reigned for almost 70 years.
Born in 1926, Princess Elizabeth became queen on the death of her father, King George VI, in 1952. She married Philip, Duke of Edinburgh, in 1947 and the couple had four children: Charles, Anne, Andrew and Edward.
A former prince of Denmark and Greece, Prince Philip was born in 1921 and served in the British Royal Navy in World War Two. He was the longest-serving consort of any British monarch, and retired from royal duties in 2017 having completed more than 22,000 solo engagements.
He died on 9 April 2021.
The Prince of Wales is the Queen's eldest son and first in line to the throne.
On 29 July 1981 he married Lady Diana Spencer, who became the Princess of Wales. The couple had two sons, William and Harry. They later separated and their marriage was dissolved in 1996. On 31 August 1997, the princess was killed in a car crash in Paris.
Prince Charles married Camilla Parker Bowles on 9 April 2005. As heir to the throne, his main duties are to support the Queen in her royal commitments.
Prince William is the elder son of the Prince of Wales and Diana, Princess of Wales, and is second in line to the throne.
The duke was 15 when his mother died. He went on to study at St Andrews University, where he met his future wife, Kate Middleton. The couple were married in 2011.
On his 21st birthday he was appointed a Counsellor of State - standing in for the Queen on official occasions. He and his wife had their first child, George, in July 2013, their second, Charlotte, in 2015 and third, Louis, in 2018.
The prince trained with the Army, Royal Navy and RAF before spending three years as an RAF search-and-rescue pilot with RAF Valley on Anglesey, north Wales. He also worked part-time for two years as a co-pilot with the East Anglian Air Ambulance alongside his royal duties. He left the role in July 2017 to take on more royal duties on behalf of the Queen and Duke of Edinburgh.
Prince George of Cambridge was born on 22 July 2013 at St Mary's Hospital in London. Prince William was present for the birth of his son, who weighed 8lb 6oz (3.8kg). He started primary school in September 2017.
Prince George is third in line to the throne, after his father and grandfather.
The Duchess of Cambridge gave birth to her second child, a girl on 2 May 2015, again at St Mary's Hospital. The Duke of Cambridge was present for the birth of the 8lb 3oz (3.7kg) baby. The duke and duchess named her Charlotte Elizabeth Diana.
She is fourth in line to the throne and is known as Her Royal Highness Princess Charlotte of Cambridge.
The Duchess of Cambridge gave birth to her third child, a boy weighing 8lbs 7oz, on 23 April, 2018 at St Mary's Hospital in London.
The Duke of Cambridge was present for the birth of Louis Arthur Charles.
Prince Harry trained at the Royal Military Academy Sandhurst and went on to become a lieutenant in the Army, serving as a helicopter pilot.
During his 10 years in the Armed Forces, Capt Wales, as he became known, saw active service in Afghanistan twice, in 2012 to 2013 as an Apache helicopter co-pilot and gunner. He left the Army in 2015 and now focuses on charitable work, including conservation in Africa and organising the Invictus Games for injured members of the armed forces.
He has been a Counsellor of State since his 21st birthday and stood in for the Queen on official duties.
He married US actress Meghan Markle on 19 May, 2018, at Windsor Castle. In January 2020, the royal couple said they would step back as "senior" royals and divide their time between the UK and North America. They said they intended to "work to become financially independent".
Just over a year later, Buckingham Palace confirmed the couple would not be returning to royal duties, and would give up their honorary military appointments and royal patronages.
The Sussexes' first child, Archie Harrison Mountbatten-Windsor, was born on 6 May 2019, weighing 7lbs 3oz, with the duke present for his birth. By naming him as they did, the couple chose not to use a title for their first born.
When the name was announced, BBC royal correspondent Jonny Dymond said the decision was a strong indication the couple did not want to bring him up as a formal royal.
The Duchess of Sussex gave birth to her second child in Santa Barbara, California. on 4 June 2021. Lilibet Diana Mountbatten-Windsor - to be known as Lili - is named after the Royal Family's nickname for the Queen and is her 11th great-grandchild.
She was given the middle name Diana in honour of Prince Harry's mother, who died in a car crash in 1997 when he was 12 years old.
Prince Andrew, ninth in line to the throne, was the third child of the Queen and Duke of Edinburgh - but the first to be born to a reigning monarch for 103 years.
He was created the Duke of York on his marriage to Sarah Ferguson, who became Duchess of York, in 1986. They had two daughters - Beatrice, in 1988, and Eugenie, in 1990. In March 1992 it was announced the duke and duchess were to separate. They divorced in 1996.
The duke served for 22 years in the Royal Navy and saw active service in the Falklands War in 1982. In addition to royal engagements, he served as a special trade representative for the government until 2011.
Prince Andrew stepped away from royal duties in 2019 after an interview with the BBC about his relationship with US financier Jeffrey Epstein, who killed himself while awaiting trial on sex-trafficking and conspiracy charges.
The duke was heavily criticised for his friendship with Epstein, but he said he did not witness any suspicious behaviour during visits to the US financier's home.
In a statement, announcing he was stepping back from public duties for the foreseeable future, the duke said he unequivocally regretted his "ill-judged association with Jeffrey Epstein".
Princess Beatrice is the elder daughter of Prince Andrew and Sarah, Duchess of York. Her full title is Her Royal Highness Princess Beatrice of York. She has no official surname, but uses the name York.
She married property tycoon Edoardo Mapelli Mozzi at The Royal Chapel of All Saints at Royal Lodge, Windsor, in July 2020. The couple had been due to marry in May, but coronavirus delayed the plans.
Princess Beatrice had a baby girl in September 2021, who becomes the 11th in line to the throne and is the Queen's 12th great-grandchild.
Princess Eugenie is the younger daughter of Prince Andrew and Sarah, Duchess of York. Her full title is Her Royal Highness Princess Eugenie of York and she is 11th in line to the throne.
Like her sister Princess Beatrice, she has no official surname, but uses "York". She married her long-term boyfriend Jack Brooksbank at Windsor Castle on 12 October 2018.
Princess Eugenie and Jack Brooksbank's son, August, born on 9 February 2021, is the Queen's ninth great-grandchild.
Prince Edward was given the title Earl of Wessex and Viscount Severn on his marriage to Sophie Rhys-Jones in 1999. The couple have two children, Lady Louise, born in 2003 and James, Viscount Severn, born in 2007.
After a brief period with the Royal Marines, the prince formed his own TV production company. He now supports the Queen in her official duties and carries out public engagements for charities. The birth of Princess Beatrice's daughter in September means he move down one place to become 14th in line to the throne.
Viscount Severn is the younger child of the Earl and Countess of Wessex. The couple decided to give their children "courtesy" titles as sons or daughters of an Earl, rather than the style prince or princess. It is thought this decision was made to avoid some of the burdens of royal titles.
Born in 2003, Lady Louise Windsor is the elder child of the Earl and Countess of Wessex.
Anne, Princess Royal is the Queen's second child and only daughter. When she was born she was third in line to the throne, but is now 17th. She was given the title Princess Royal in June 1987.
Princess Anne has married twice; her first husband Captain Mark Phillips is the father of her two children, Peter and Zara, while her second is Vice-Admiral Timothy Laurence.
The princess was the first royal to use the surname Mountbatten-Windsor in an official document, in the marriage register after her wedding to Capt Phillips. She competed in equestrian events for Great Britain in the 1976 Montreal Olympics and is involved with a number of charities, including Save the Children, of which she has been president since 1970.
Peter Phillips is the eldest of the Queen's grandchildren. He married Canadian Autumn Kelly in 2008 and together they have two daughters, Savannah, born in 2010, and Isla, born in 2012.
The children of the Princess Royal do not have royal titles, as they are descended from the female line. Mark Phillips refused the offer of an earldom when he married so their children do not have courtesy titles.
Peter Phillips and his wife announced they were getting divorced in February 2020.
Savannah, born in 2010, is the elder daughter of Peter and Autumn Phillips and the Queen's first great-grandchild.
Isla, born in 2012, is the second daughter of Peter and Autumn Phillips.
Zara Tindall followed her mother and father with a highly successful riding career - including winning a silver medal at the London 2012 Olympics. She married former England rugby player Mike Tindall in 2011 and the couple had their first child, Mia Grace, in 2014.
The children of the Princess Royal do not hold a royal title, as they are descended from the female line, but she remains 21st in line to the throne. Their father, Mark Phillips, turned down an earldom when he married Princess Anne, so they do not have courtesy titles.
The Queen's granddaughter Zara Tindall gave birth to her first child, Mia Grace, in January 2014.
The couple's second child - the Queen's seventh great-grandchild - was born on 18 June 2018 at Stroud Maternity Unit, Gloucestershire, weighing 9lb 3oz.
Lena Elizabeth was named in honour of her great-grandmother.
Like her sister, Lena Elizabeth does not have a royal title and so will also be known as Miss Tindall.