The Queen's official birthday is marked each year by a colourful military parade and march-past known as Trooping the Colour.

The event takes place each June in London on Horse Guards Parade, the military parade ground between St James's Park and Whitehall. Many tourists and Londoners join the huge crowds to watch the event - which this year takes place on 13 June - from the Mall and the nearby Park and it is enjoyed by millions of people on television worldwide.

The custom of Trooping the Colour dates back to the time of Charles II in the 17th century when the colour, or flag, of a regiment was used as a rallying point in battle. The colour was trooped, or carried along the ranks, each day to make sure that every man could recognise those of his own regiment.

• Colour always honoured

A regiment's colour has always been honoured as it represents the direct link of service to the sovereign, as well as to fallen soldiers and officers. Its loss or capture on the battlefield was considered the greatest shame. Conversely the capture of an enemy colour was deemed the greatest glory.

It is a great honour for a young officer to carry the colour as, historically, only the most courageous Ensigns were assigned to carry the regiment's colour in battle. Nowadays it is usually carried by a Second Lieutenant who is good at drill and ceremonial and is physically fit!

• Troops from the Household Division

The soldiers on parade are trained and operational troops drawn from what is known as the Household Division - the Foot Guards and Household Cavalry, and the King's Troop.

Only one colour can be trooped at a time and the five Household Regiments - Grenadier, Coldstream, Scots, Irish and Welsh Guards - take their turn each year.

Apart from 1955 when the event was cancelled, the Queen has attended the Trooping in every year of her reign. Until 1987 she rode side-saddle wearing the uniform of the regiment whose colour was being trooped. She now rides to and from the ceremony in a carriage and takes the Royal Salute on a dais in front of Horse Guards.

• Massed bands

The parade begins with her inspection and then the colour is trooped to the accompaniment of massed bands, some mounted, some on foot. The bands play the Queen back to Buckingham Palace down the Mall.

After the ceremony the Royal Family gathers on the Palace balcony where they watch a flypast by the Royal Air Force.

• Seats publicly available

Many of the seats for Trooping are allocated to various dignitaries, but it is possible for members of the public to get hold of tickets. These are allocated by a ballot for which people apply in January and February each year.