The wedding of Prince William and Catherine Middleton took place on Friday, 29 April 2011 at Westminster Abbey in London, England. William was second in the line of succession to the British throne at the time, later becoming heir apparent. The couple had been in a relationship since 2003.

John Hall, Dean of Westminster, presided at the service; Rowan Williams, Archbishop of Canterbury, conducted the marriage; Richard Chartres, Bishop of London, preached the sermon; and a reading was given by Catherine's brother James. William's best man was his brother Prince Harry, while Catherine's sister Pippa was the maid of honour. The ceremony was attended by the bride's and groom's families, as well as members of foreign royal families, diplomats, and the couple's chosen personal guests. After the ceremony, the couple made the traditional appearance on the balcony of Buckingham Palace. As William was not the heir apparent to the throne at the time, the wedding was not a full state occasion, and details such as much of the guest list of about 1,900 were left for the couple to decide.

William and Catherine first met in 2001. Their engagement, which took place on 20 October 2010, was announced on 16 November 2010. The build-up to the wedding and the occasion itself attracted much media attention, being compared in many ways with the wedding of William's parents in 1981. The occasion was made a public holiday in the United Kingdom and featured many ceremonial aspects, including use of the state carriages and roles for the Foot Guards and Household Cavalry. Events were held around the Commonwealth to mark the wedding; organisations and hotels held events across Canada, over 5,000 street parties were held throughout the United Kingdom, and about a million people lined the route between Westminster Abbey and Buckingham Palace on the wedding day. The ceremony was viewed live by tens of millions more around the world, including 72 million live streams on YouTube. In the United Kingdom, television audiences peaked at 26.3 million viewers, with 36.7 million watching at least part of the coverage.

Prince William and Catherine Middleton first met in 2001 while studying at the University of St Andrews. They began dating in 2003. On 16 November 2010, Clarence House stated that William was to marry Catherine "in the Spring or Summer of 2011, in London". They were engaged in October 2010, while on a private holiday in Kenya; William gave Middleton the same engagement ring that his father had given to William's mother, Diana, Princess of Wales—an 18-karat white gold ring with a 12-carat oval Ceylon (Sri Lankan) sapphire and 14 round diamonds. It was announced at approximately the same time that, after their marriage, the couple would live on the Isle of Anglesey in Wales, where William was based with the Royal Air Force.

The Queen said she was "absolutely delighted" for the couple, giving her formal consent to the marriage, as required by the since-repealed Royal Marriages Act 1772, in her British privy council on the morning of the engagement. Congratulations also came in from the Queen's prime ministers, including Julia Gillard, Prime Minister of Australia, who had at other times demonstrated moderate republican leanings. The suffragan Bishop of Willesden, Pete Broadbent, who also has republican views, published a critical reaction to the wedding announcement on Facebook. He later acknowledged that his words were "offensive" and apologised, but his superior, Richard Chartres, Bishop of London, instructed him to withdraw from public ministry "until further notice".

Following the announcement, the couple gave an exclusive interview to ITV News political editor Tom Bradby and hosted a photocall at St James's Palace. On 12 December 2010, Buckingham Palace issued the official engagement photographs; these were taken on 25 November, in the state apartments at St. James's Palace, by photographer Mario Testino.

On 23 November 2010, the date of the ceremony was confirmed as Friday, 29 April 2011. The Queen in her British Council ordered on 15 December 2010 that the wedding day would be a public holiday throughout the United Kingdom. It was also declared an official public holiday in the British Overseas Territories of Bermuda, the Cayman Islands, Gibraltar, the Falkland Islands, Montserrat, and the Turks and Caicos, and the British Crown Dependencies of Guernsey, Jersey, and the Isle of Man. As 29 April fell six days before elections for the Scottish Parliament and the Alternative Vote referendum, this attracted political comment. John Curtice, a professor of politics at the University of Strathclyde, stated for the Scottish elections that the date was "unfortunate" and was "likely to see the Royal Family getting caught up in political debate".

Middleton, who was christened as a child, decided to be confirmed into the Church of England preceding her wedding. The confirmation service was conducted on 10 March at St James's Palace by the Bishop of London with her family and William in attendance. TV programmes were also shown in the UK prior to the wedding which provided deeper insights into the couple's relationship and backgrounds, including When Kate Met William and Channel 4's Meet the Middletons.