It's one of the most eagerly-anticipated events in the royal calendar, and is rumoured to be one the Queen's favourites.
After all, Trooping the Colour is essentially put on to celebrate her official birthday.
For avid royal watchers, it's also a prime opportunity to see the royals - old and young - en masse.
Later today, the Duchess of Sussex will be attending, making it her first engagement since the birth of baby Archie. She made her debut last year - which coincided with the Duchess of Cambridge's first public engagement following the birth of Prince Louis.
However nervous Meghan and Kate might have felt, these appearances went A LOT more smoothly than Diana's first Trooping the Colour.
Back in 1981, the then Lady Diana was just 19 years-old, and mere weeks away from marrying into the Royal family.
A shy teenager who later described herself as a "fat Sloane Ranger", her first Trooping of the Colour could not have been more dramatic.
It was the year someone fired a gun at the Queen.
At that time, the Queen, being a keen equestrian, led the Household Cavalry through central London, riding sidesaddle on her mare Burmese.
However, as she approached the junction of the Mall and Horseguards Parade, six shots rang out.
The gunman was 17 year-old Marcus Serjeant, the BBC reports.
It was only blanks which were being fired from a starting gun, luckily, meaning no one was hurt - although the Queen's mare did get startled.
Although shaken herself, fortunately, the Queen was able to calm the horse down and get back in control in a matter of seconds.
The procession continued as planned, and afterwards the Queen returned to Buckingham Palace by the same route, under the close watch of security services.
Serjeant was quickly pounced upon by the police, and later convicted of treason and sentenced to five years in prison.
He has since admitted "I wanted to be famous. I wanted to be a somebody."
