On paper, the idea of Third Stream is simple: jazz and classical music, mixed together—not in a way meant to supersede jazz or classical but as, in the words of composer Gunther Schuller, “another option amongst many for today’s creative musicians.” Of course, those musicians took a simple concept and used it as a launchpad to create records that are deep, dynamic, and complex, exploring new possibilities for melody and improvisation. Schuller coined the term in 1957, but this playlist starts earlier, beginning the story of Third Stream with the orchestral innovations of hybrid composers like George Gershwin and Duke Ellington. The Modern Jazz Quartet, meanwhile, take center stage, emerging from Dizzy Gillespie’s rhythm section in the early ’50s, using John Lewis’s subtly swinging piano and Milt Jackson’s unpredictable vibraphone to explore new possibilities in fusion, crossing from the conservatory to the nightclub and back again.