As second in line to the British Throne, Prince William attends a number of important royal occasions such as Trooping the Colour and Remembrance Day at the Cenotaph.
Prince William lays a wreath
On his 21st birthday, William became a Counsellor of State.
This means that the Queen can ask him to take over some of her duties if she is abroad or ill for more than a few days.
Prince William first represented the Queen at an event in July 2005, when he attended ceremonies to mark the 60th Anniversary of the Second World War in New Zealand.
The prince also goes to events put on by charities and organisations which work for things he cares about.
One of these is the homelessness charity Centrepoint. His mother Diana, Princess of Wales was also Patron of the charity.
In 2006, he took over from his uncle, The Duke of York, as President of The FA in May 2006 on the day of the FA Cup Final.
On St George's Day, 23 April 2008, The Queen appointed him a Royal Knight Companion of the Most Noble Order of the Garter.
The prince has twice run a mile for Sport Relief, and also hit the road with his brother Harry for a 1,000 mile charity motorbike ride across South Africa.