A history of the design and achievements of the high-speed, 1950s-era X-15 airplane is presented. The following chapters are included: A New Science; A Hypersonic Research Airplane; Conflict and Innovation; The Million-Horsepower Engine; High Range and Dry Lakes; Preparations; The Flight Program; and the Research Program. Selected biographies, flight logs and physical characteristics of the X-15 Airplane are included in the appendices