For Leonard Bernstein, music was a language capable of communicating more directly than in words, and jazz was a crucial part of his musical vocabulary. As an idiom made up of a range of styles--whether stride, boogie-woogie, swing, bebop, or cool--jazz was central to Bernstein’s compositional aesthetic, particularly in his approach to tonality and to defining American music. The blues, as a special part of this jazz idiom, also helped Bernstein articulate a personal identity, expressing everything from sensuality to humor to loss and isolation. This book will examine the shifting meanings of Bernstein’s jazz language in theatrical and symphonic works from across his career. His commitment to jazz in works like On the Town, West Side Story, and Mass also demonstrates Bernstein’s conviction that music could be socially engaged and that jazz was one of the most effective means of engagement. The plurality of jazz styles in Bernstein’s music resonates with many of America’s most significant political and cultural questions, including shifts in the relationship between African American and Jewish American identities. The language of jazz helped Bernstein find a voice in the political and musical senses and continually rearticulate his own American musical identity.