"Jack and Jill" (sometimes "Jack and Gill", particularly in earlier versions) is a traditional English nursery rhyme. The Roud Folk Song Index classifies the commonest tune and its variations as number 10266, although it has been set to several others. The original rhyme dates back to the 18th century and different numbers of verses were later added, each with variations in the wording. Throughout the 19th century new versions of the story were written featuring different incidents. A number of theories continue to be advanced to explain the rhyme's historical origin.