This article examines the development of Top 40 radio by Todd Storz and Mid- Continent Broadcasting in the years following World War II. Our findings, based on recent interviews we have conducted with Storz employees, challenge the received wisdom concerning Top 40's development and practices. Previous accounts infer that Top 40 marked an abrupt, almost instantaneous break with previous radio programming practice; that on-air talent chafed under its tightly prescribed scheduling; and that Top 40 specifically targeted the burgeoning teenage audience, primarily through rock-and-roll music programming. We find, instead, that Top 40's development was gradual; that deejays at Storz stations readily embraced the format, and that Storz stations, rather than seeking specific demographic segments, sought to re-aggregate the mass audience for radio. We argue that Top 40 radio was conceived in mechanistic, rather than aesthetic, terms. Each Storz station functioned as a well-oiled sales machine; the intention was to sell the station-as-brand to advertisers, rather than promote individual records or personalities to audiences.