This text contains Arnold Schoenberg's thoughts on classical and romantic harmony. It presents a resume of the principles of the ''Theory of Harmony'', then demonstrates the concept of ''monotonality''. The music examples range from the entire development sections of classical symphonies. Ninety integrated music examples range fromthe entire development sections of classical symphonies to analyses of the harmonic progressions of Strauss, Debussy, Reger and his own early music.