Abstract What does Mallarmé mean when he describes the book as an ‘instrument spirituel’? What does this idea tell us about his understanding of subjectivity? Analysing a selection of Mallarmé’s prose writings from Divagations (1897) and his pedagogical work L’Anglais récréatif (from the late 1870s), this article answers these questions in three sections. First, it considers Mallarmé’s speculative theorizations of the book, as it argues that the book is both a place and an event. Next, the article analyses the ‘practice of the book’, detailing how readers and writers engage with the book (and its worlds). Finally, the article draws on Gilbert Simondon’s writings about technology (Du mode d’existence des objets techniques (1958) and ‘Cultur...