Henley Royal Regatta (or Henley Regatta, its original name pre-dating Royal patronage) is a rowing event held annually on the River Thames by the town of Henley-on-Thames, England. It was established on 26 March 1839. It differs from the three other regattas rowed over approximately the same course, Henley Women's Regatta, Henley Masters Regatta, and Henley Town and Visitors' Regatta, each of which is an entirely separate event.

The regatta lasts for five days (Wednesday to Sunday) ending on the first weekend in July. Races are head-to-head knock out competitions, raced over a course of 1 mile 550 yards (2,112 m). The regatta regularly attracts international crews to race. The most prestigious event at the regatta is the Grand Challenge Cup for Men's Eights, which has been awarded since the regatta was first staged.As the regatta pre-dates any national or international rowing organisation, it has its own rules and organisation, although it is recognised by both British Rowing (the governing body of rowing in England and Wales) and FISA (the International Federation of Rowing Associations). The regatta is organised by a self-perpetuating body of Stewards, who are largely former rowers themselves. One exception to this rule is that the Mayor of Henley-on Thames Council is an ex-officio Steward. Pierre de Coubertin modelled elements of the organisation of the International Olympic Committee on the Henley Stewards.The regatta is regarded as part of the English social season. As with other events in the season, certain enclosures at the regatta have strict dress codes.