The Duke and Duchess of Cambridge have introduced their daughter to the world, as they left hospital to take her home to Kensington Palace.
The princess, whose name has yet to be announced, slept in her mother's arms during her first public appearance outside St Mary's Hospital, in London.
The princess - who is fourth in line to the throne - was delivered at 8.34am BST on Saturday (about 9.30pm NZST) after a short labour.
The Duke of Cambridge was present for the birth of the 3.7kg baby.
The couple emerged from the hospital to crowds of well-wishers and the world's media. They stood on the steps briefly before heading back into the hospital to put the princess in a car seat. Prince William then drove them to Kensington Palace.
They did not speak to the media.
The baby was born less than three hours after the couple arrived at the private Lindo Wing at St Mary's Hospital and the duchess had been in hospital for just over 12 hours before leaving.
The family will stay for a few days at Kensington Palace before decamping to their country home, Anmer Hall on the Sandringham estate in Norfolk.
The duchess was admitted to the hospital in Paddington, west London, at about 6am BST. The birth announcement came about 11am BST, and the couple left the hospital with their daughter shortly after 6pm BST.
While the birth was announced on Twitter, there was still room for tradition with an easel announcing the birth placed in the courtyard of Buckingham Palace.
The birth was also proclaimed by a town crier who was not on official duty but certainly entertained the crowds outside the hospital.
Prince William left the hospital briefly in the afternoon to pick up his 21-month-old son and told the waiting crowds the couple were "very happy".
Prince George appeared to be the only visitor and he was later taken home ahead of his parents and little sister.
In a statement, Kensington Palace said: "Their Royal Highnesses would like to thank all staff at the hospital for the care and treatment they have all received.
"They would also like to thank everyone for their warm wishes."
Gun salutes will be fired in Hyde Park and at the Tower of London on Monday to mark the birth.
Messages of congratulations poured in throughout the day for the couple and their second child, including ones from British Prime Minister David Cameron and the Archbishop of Canterbury Justin Welby.
Congratulations to the Duke and Duchess of Cambridge on the birth of their baby girl. I'm absolutely delighted for them.— David Cameron (@David_Cameron) May 2, 2015
Britain's Deputy Prime Minister Nick Clegg tweeted that he and his wife Miriam wished the family "all the best".
Britain's Labour leader Ed Miliband wrote: "Congratulations to the Duke and Duchess on the birth of their daughter. Wishing them lots of joy and happiness - and hopefully some sleep!"
The latest royal joins the line of succession behind her grandfather Prince Charles, father Prince William and brother Prince George.
She will not be overtaken in the line of succession by any future younger brothers.
Under new rules which came into force in March, male bias was removed from the succession rules. The princess will also be able to marry a Roman Catholic without losing her place in line to the throne.
Prince Charles, who had earlier said he was hoping for a grand-daughter, and the Duchess of Cornwall said they were "absolutely delighted".
In addition to the die-hard royal fans, who had been camping outside the hospital in Paddington for days, hundreds of well-wishers descended when the news first broke that the duchess had been admitted to hospital.
The next news to be announced is likely to be the name of the princess, who is the Queen's fifth great-grandchild.
Alice is the favourite with several bookmakers, although Charlotte, Elizabeth and Victoria have also been popular with punters.
Prince George's name was announced two days after his birth in July 2013, which is a relatively quick turnaround compared with previous royal babies.
It was seven days before the name of a newborn Prince William was announced in 1982, and there was a wait of a month following Prince Charles' birth in 1948.
Gift from New Zealand
Prime Minister John Key said he would like to congratulate Prince William, Catherine and Prince George on their wonderful news on behalf of the people of New Zealand.
He also extended his congratulations to the Queen and Prince Phillip, and the grandparents - the Prince of Wales and Duchess of Cornwall.
The Governor-General, Lieutenant General Sir Jerry Mateparae, also sent his congratulations, saying he was delighted at the news of the birth.
New Zealand's official gift to the royal couple will be a selection of woollen baby items from Hutt Valley company Stansborough, including a pelt teddy bear.
Stansborough director Cheryl Eldridge said the company was honoured its products were chosen and she was ecstatic her company's products were chosen over so many other things.
Stansborough designed and wove the textiles for the Lord of the Rings and Hobbit movies.
New Zealand Post said 1000 special edition coins will also be minted to mark the birth.
A 21-gun salute will be fired from Point Jerningham in Wellington at midday on Monday to celebrate the birth.
The Sky Tower is currently flashing between shades of pink and blue in anticipation of the new #RoyalBaby.— Monarchy New Zealand (@monarchynz) May 2, 2015