The Sovereign's birthday is officially celebrated by the ceremony of Trooping the Colour on a Saturday in June.
This year Trooping the Colour took place on 11 June 2011. The Queen's Colour of the 1st Battalion Scots Guards was trooped.
Although The Queen was born on 21 April, it has long been the tradition to celebrate the Sovereign's birthday publicly on a day in the summer, when good weather is more likely.
Trooping the Colour is carried out by fully trained and operational troops from the Household Division (Foot Guards and Household Cavalry) on Horse Guards Parade in Whitehall, watched by members of the Royal Family, invited guests and members of the public.