The popularity of the motion picture soundtrack O Brother, Where Art Thou? brought an extraordinary amount of attention to bluegrass, but it also drew its share of criticism from some aficionados who felt the album's inclusion of more modern tracks misrepresented the genre. This soundtrack, these purists argued, wasn't bluegrass, but “roots music,” a new and, indeed, more overarching category concocted by journalists and marketers. Why is it that popular music genres like these and others are so passionately contested? And how is it that these genres emerge, coalesce, change, and die out? This book provides new understanding as to why we debate music categories, and why those terms are unstable and always shifting. To tackle the full complexity of genres in popular music, the author embarks on a wide-ranging collection of case studies. Here he examines not only the different reactions to O Brother, but also the impact of rock and roll's explosion in the 1950s and 1960s on country music and jazz, and how the jazz and indie music scenes in Chicago have intermingled to expand the borders of their respective genres. Throughout, the author finds that genres are an integral part of musical culture—fundamental both to musical practice and experience, and to the social organization of musical life.