When an athlete takes the Olympic oath at the opening ceremony, he/she commits, on behalf of all the other competitors, to respect the rules and take part the competitions in a spirit of fair play.
The reciting of the Olympic oath by an athlete has been one of the protocol elements of the opening ceremony since the 1920 Games in Antwerp. The text, originally written by Pierre de Coubertin, has since evolved. Since the 2000 Games in Sydney, it has included a sentence committing to sport without doping.
These days, as well as on behalf of the athletes, the Olympic oath is taken on behalf of the officials and coaches.