A dress code lets the host guarantee the unity of the evening, and lets the visitor know exactly what is expected before walking through the door. On the invitations recorded by this site, it runs from the most relaxed to the strictest: smart casual with a hat recommended at the polo, all-white dress required at the summer white parties, strict jacket and tie at the Qatar Prix de l'Arc de Triomphe, on October 3 and 4, 2026 at ParisLongchamp, evening dress and black tie for galas, up to the tailcoat of the great Viennese balls. Three things to know. First, it is applied to the letter: La Scala refuses spectators in shorts or tank tops entry to the auditorium, without refunding the ticket, and the Stewards' Enclosure at Henley refuses entry to women whose hemline does not fall below the knee. Second, it can be measured in numbers: in the Royal Enclosure at Royal Ascot, hats are compulsory for women and a headpiece is accepted only if its base is at least 10 cm in diameter. Finally, it varies by enclosure within a single event: at Royal Ascot 2027, from June 15 to 19, the Windsor Enclosure (from £25) imposes no formal dress code, while the Queen Anne and the Royal Enclosure apply theirs strictly.