American popular music history takes a new shape when the force behind the hits – radio airplay – claims center stage. The 1950s Top 40 hits approach structured rival formats, too, by the 1970s: rhythm & blues, country, adult contemporary, and rock. This resulted in multiple mainstreams, overlapping centers that explain why pop multiplicity, not rock monoculture, won out by the 1990s. An introduction explores how formats, which pragmatically unite sets of listeners with sets of sounds, are different than genres, which turn on musical ideals. Five case studies then examine particular formats through artists, record labels, and radio stations. The Isley Brothers illustrate how, from early soul to hip-hop, R&B and Top 40 created corporate, mediated rituals of black expression. Dolly Parton’s leap from country to adult contemporary success illustrates Nashville centrism filtering the modern for white southerners. A&M Records’ unlikely hitmakers (Herb Alpert, Carpenters, Peter Frampton, the Police, Amy Grant), demonstrate the calculated diversity, but also precarity, of adult-oriented middle of the road. Elton John’s thirty-year run of Top 40 success reveals a format of outsiders opting in where rockers opted out, coded gay identity, and a British Invasion becoming globalization. Hard rock Cleveland station WMMS, “the Buzzard,” thundered blue-collar rock ideals of cross-class masculinity, tested by the arrival of the yuppie. A final chapter, on formats in the 2000s, notes Latin programming and a surprise: technological upheaval brought Top 40 back to its most potent position in years.