In this article, the author discusses what he terms the Apollonian and Dionysian aspects of Iannis Xenakis' thought processes as reflected through his writing and music. He notes that there is an interesting separation between Xenakis the writer/theorist and Xenakis the composer/musician. The author reflects on many issues: Xenakis' notions of 'abstraction' that occupy a central position in his thought, his theory concerning the relationship between music and the sciences, his concept of 'formalisation', the complexity of Xenakis' inspiration, his underlying view of nature, his search for immediate expression, his notions of time and space, and his emphasis on creativity.