More than eight decades after his death, George Gershwin remains an outsize figure in the story of instrumental jazz. “I Got Rhythm” (1930), a popular hit from the musical Girl Crazy, provided an essential template over which swing musicians such as Lester Young etched free-wheeling improvisations during the 1930s. “I Got Rhythm” continued its prominence in the 1940s, when its melody and harmonies were reworked by the likes of Thelonius Monk and Charlie Parker. Over time, musicians streamlined Gershwin’s original composition into a standard form known as “rhythm changes.” This thirty-two-bar, AABA chord progression became a template to rival the twelve-bar blues as a jam-session cornerstone. In the 1950s, Gershwin’s compositions spurred explorations of modal jazz, as on Miles Davis’s and Gil Evans’s album-length reinterpretation of the opera Porgy and Bess (1958).