Iannis Xenakis’s Herma, for piano solo, was composed in 1960-61 and premiered in 1962, in Tokyo, by Yuji Takahashi, to whom the work is dedicated. According to the composer, Herma means ‘bond’ but also ‘foundation’ or ‘embryo’, etc. Relying on documents consulted in the Xenakis Archives, this article provides new insights into how Xenakis conceived his first piano work. It shows the relationship between Herma and one of the composer’s earlier pieces, Achorripsis, and offers a new understanding of what may have caused some of the discrepancies between the theory on which Herma is based and its application in the score.