The modal theory stems from a work by George Russell. Miles Davis introduced the concept to the greater jazz world with Kind of Blue (1959), an exploration of the possibilities of modal jazz and the best selling jazz album of all time. In contrast to Davis' earlier work with hard bop and its complex chord progression and improvisation,[129] the entire album was composed as a series of modal sketches, in which each performer was given a set of scales that defined the parameters of their improvisation and style.[130] Davis recalled: "I didn't write out the music for Kind of Blue, but brought in sketches for what everybody was supposed to play because I wanted a lot of spontaneity