The monarch, who is a passionate horse owner, was greeted with cheers as she rode into the famous racecourse in a carriage with the Prince of Wales and the Duchess of Cornwall.
Ascot hosts the famous five-day meeting which is as much a social event as an important sporting fixture that attracts some of the best thoroughbreds, jockeys and trainers in the world.
The Queen wrote in the official programme: "I was fortunate enough to own a winner at last year's royal meeting, so I know what a thrill it is to have success at this wonderful racecourse, whether you are a trainer, jockey, or one of the many hard-working stable staff associated with every runner.
"I would like to wish all those involved the very best of luck."
More top news
Police say it is "too early" to know if the body is that of journalist Kim Wall, who is believed to have died on board an amateur submarine.
'I'm not a fan of the new pound coin, but then again, I hate all change'
In a policy speech on Afghanistan, Donald Trump has performed the greatest reversal so far of his young and wild Presidency.