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
Around 88% of economists questioned by Ipsos Mori said leaving the EU would damage Britain's growth rates over the next five years.
Justice Secretary Michael Gove warned David Cameron that his failure to limit migration is 'corrosive' to public trust.
After a lively start to the long weekend with torrential, thundery downpours - a drier night.