Ton de Leeuw basically wrote Music of the Twentieth Century in the period 1961 to 1962, a time of considerable change, both in contemporary music and in the author's own life. The strong post-1945 emphasis on concerted radical structural innovation of music had however largely passed. New music was opening up in many new ways to many worlds of music, both past and present.

In 1961, De Leeuw travelled to India with a commission from the Dutch Ministry of Education, Arts and Sciences to explore the possibilities of crosscultural artistic interaction. He shared a positive outlook on this type of interaction with other composers and ‘culture makers’ in a time of de-colonialisation. The trip to India reinforced De Leeuw's awareness of the polarity that had once been associated with ‘East’ and ‘West’. De Leeuw at that time considered this to be one of the major defining issues of contemporary Western art. On the one hand, he pointed to the exaggerated cult of personality, and on the other, to a way of life which he characterised as a liberation from subjective individualism, and as a ‘return to original being’. He illustrates this notion in chapter 6, in an account of Zen archery in Japan. Although he does not explicitly advocate either attitude in this book – which he does, for example, in many of his other texts – it is clear from his wording that his sympathy rests with the latter.

Parallel to this polarity, he also compares the musical practices which directly relate to romantic aesthetics, the central notion of which he describes as a ‘servitude to oneself ‘, with those that preceded and followed it. One of his motives for writing this book was to wean his readers away from romantic aesthetics, which had already lost much of its vitality and relevance, and toward the opening of their ears to unheard worlds of music, such as the work of Debussy and Webern, which is sometimes described as where ‘silence becomes audible’. De Leeuw focuses on both of these interrelated polarities. Musically, the polarities consist of, for example, harmonic tonality on the one hand, and melodic and rhythmic modality on the other, not only in relation to music structure, but also as an expression of general attitudes toward life.