Some of the lyrics were written by Ira Gershwin alone(It Ain't Necessarily So, There's a Boat that's Leavin' for New York), and some by Ira and DuBose Heyward in collaboration(I Loves You Porgy, Bess, You is My Woman Now). However, most of the lyrics were written by Heyward as verse, and set to music by George Gershwin. There was only one song, "I Got Plenty O" Nothin" where Heyward set lyrics to   a tune.

For many years, "Porgy and Bess" was not performed much because it many of the characters were thought to be racial stereotypes--it wasn't until the full opera was finally performed in 1976 that it's full depth was appreciated. However, the original rights for Heyward's play were purchase by Al Jolson, who wanted Rodgers and Hammerstein to create a musical that he could perform in blackface. If that had happened--