How did jazz take shape? Why does jazz have so many styles? Why do jazz songs get longer as the twentieth century proceeds? Marc Myers, in his fascinating book Why Jazz Happened (University of California Press, 2014) examines the social and economic forces affected the growth of jazz between 1942 and 1972. Myers considers how the American Federation of Musicians ban on recording in 1942 changes the terrain for jazz musicians. He looks to how the G.I. Bill and suburbanization bring a new adult sophistication to the music. Myers also explores how changes in recording technology allow jazz artists a greater range of expression and permits the recording of longer songs and extended soloing. The book culminates with considering how jazz musicians responded to the challenge offered by rock music.