When some months before publication of the first issue of Organised Sound, Iannis Xenakis sent the editors a previously unpublished set of lecture notes for possible inclusion in the journal, it seemed natural to locate the resulting article within the present issue, whose major theme is 'algorithmic composition' (AC). Whilst Xenakis himself does not use this term, it is evident that he has had a major influence on those who do, as evidenced by his citations in most of the other articles in this issue. Not only has Xenakis been an original thinker in this domain, his article as presented here also illuminates many of his compositional practices, indicated as the working-out of probabilistic formulae. The article ranges wildely, with a section on the UPIC system, and we believe it also captures much of the empathetic, intensely enquiring nature of a mind deeply versed in both scientific and artistic modes of humanist thought.