The decathlon is an athletic event consisting of ten track and field events. The word decathlon is of Greek origin (from δέκα deka [ten] and αθλος athlos [contest]). Events are held over two consecutive days and the winners are determined by the combined performance in all. Performance is judged on a points system in each event, not by the position achieved. The decathlon is contested mainly by male athletes, while female athletes contest the heptathlon.

Traditionally, the title of "World's Greatest Athlete" has been given to the man who wins the decathlon. This began when King Gustav V of Sweden told Jim Thorpe, "You, sir, are the world's greatest athlete" after Thorpe won the decathlon at the Stockholm Olympics in 1912. The current holder of the title is American Bryan Clay, the gold medal winner of the event at the 2008 Beijing Olympics, who took the title from Athens Olympics Czech champion Roman Šebrle.