Prince George was christened in a ceremony that spanned four generations of the royal family and included three future kings.
The ceremony was held in the historic Chapel Royal at St James's Palace.
It had clearly been a joyful family occasion for the royals and Kate's family, the Middletons.
George arrived for his christening in the arms of his father, the Duke of Cambridge.
The three-month-old was making only his second appearance in public for the christening.
His only previous public outing was when William and Kate left the Lindo Wing of St Mary's Hospital in central London the day after he was born on 22 July.
On that occasion, they proudly showed him off to the world's media and could not contain their joy as he slept peacefully.
Since then his father has revealed that George has a good pair of lungs on him, but he appeared to be on his best behaviour for his first official engagement.
His private christening, like his birth, has attracted interest from across the globe.
The Archbishop of Canterbury, the Most Rev Justin Welby, greeted both families at the chapel in central London.
Kate looked relaxed before the service began and wore a cream Alexander McQueen outfit and a matching hat by milliner Jane Taylor.
Prince William told onlookers his son was "all ready" for the big occasion, adding: "So far so good".
George wore a replica of a christening gown made for Queen Victoria's eldest daughter in 1841, which almost touched the ground.
He has seven godparents, including Zara Phillips and six of his parents' close friends.
Kensington Palace revealed William and Kate chose two hymns, two lessons and two anthems for the service.
The first lesson, from the Gospel of St Luke, Ch 18, verses 15-17, was read by Pippa Middleton, Kate's sister and her maid of honour at the couple's wedding.
The second, from St John's gospel, chapter 15, verses 1-5, was read by Prince Harry.
The two hymns at the service were Breathe on Me, Breath of God and Be Thou My Vision.
Two anthems were also performed at the service, including Blessed Jesu! Here we Stand, by Richard Popplewell, which was written for William's own baptism in 1982.
The second was John Rutter's well-known anthem The Lord Bless You and Keep You.
Both were performed by The Choir of Her Majesty's Chapel Royal, which performed at the royal couple's wedding as well as at the Golden and Diamond Jubilee Services at St Paul's Cathedral.
The Archbishop of Canterbury was supported by The Dean of The Chapel Royal (The Right Reverend and Right Honourable Richard Chartres) and The Sub-Dean of the Chapel Royal (The Reverend Prebendary William Scott).