How did George and Ira Gershwin divide their work when writing songs?

The songwriting partnership between George and Ira Gershwin was unique because it typically reversed the standard industry process: George’s melodies almost always came first.1

George, a prolific composer, often created quality melodies through spontaneous improvisation or by drawing from his extensive notebooks of "good tune" sketches. Once George provided the melody, Ira would spend a week or more meticulously fitting lyrics to the music. Ira was known for his precision, polishing each line until he was satisfied, which earned him the nickname "The Jeweller" among his peers. This process required Ira to be brilliant while working within the highly confining rhythms and accents established by George’s compositions.1

When asked about their creative order, Ira famously quipped that the first thing to come was "the contract". Together, the brothers collaborated on more than 20 Broadway musicals and motion pictures, creating numerous standards that remain iconic in American music.12