Prince Harry, who organised the games, said "lives will be changed". He told the crowd: "Over the next four days we will see some truly remarkable achievements."
More than 400 competitors, from 13 countries, will go head to head in nine adaptive sports over four days.
There were also displays by military units including the King's Troop Royal Horse Artillery.
After Prince Harry's speech, three singers from the Armed Forces performed the Invictus Anthem, written by Coldplay frontman Chris Martin. They were joined by the Urban Voices Collective,
The Invictus Games for wounded servicemen and women have opened at the Queen Elizabeth Olympic Park in London.
The Duke of Cambridge, the Duchess of Cornwall and the Prince of Wales attended the opening ceremony, along with Prince Harry and 6,500 spectators.
You can catch all of the sporting action over the next four days on the BBC.
In a recorded message, US President Barack Obama's wife, Michelle, told competitors: "Some of the most inspiring moments I have had as First Lady have been when I have met with wounded warriors like so many of you."
The event began with a short version of God Save the Queen, followed by the Invictus fanfare and an amazing flypast by the Red Arrows.
Great Britain, seen here entering the opening ceremony.
The countries taking part are: Afghanistan, Australia, Canada, Denmark, Estonia, France, Italy, Georgia, Germany, the Netherlands, New Zealand, USA and...
