The Great American Songbook was built over a five-decade period beginning in the 1920s as a sprawling, unofficial canon of songs mostly from Broadway and Hollywood musicals as well as Tin Pan Alley. George and Ira Gershwin, Cole Porter, and Irving Berlin—among others—penned tunes reflecting upon love and its travails with uncommon poetic economy. Their handiwork is woven deeply into the fabric of American culture, forming the standard catalog for singers like Frank Sinatra and Tony Bennett. Lyrically erudite, melodically sophisticated, and harmonically rich, the material is a proving ground for true stylists. Equally important, those songs have long served as repertoire in jazz, a deep collection of popular works custom-built for harmonic and melodic investigation by singers like Ella Fitzgerald and Louis Armstrong and instrumentalists such as Sonny Rollins and Charlie Parker. And contemporary artists continue to draw from the songbook, be it Lady Gaga or Robert Glasper.