It was written by George and Ira Gershwin in 1935 and was one of the songs in "Porgy and Bess". Check the following page: http://www.sju.edu/~bs065903/gershwin/plays/porgy.htm

The song has been covered by lots of singers but I can't remember the name of the one who did the very staccato pop version back in the '70s (I think). I just heard it recently.