In this article, we seek to clarify the historical and philosophical roots of Bion’s somewhat enigmatic concept of reverie. We also reflect on the rhetorical reasons for Bion’s decision to introduce the concept into psychotherapeutic discourse. Although Josef Breuer and Sigmund Freud (1894) had used the term in their Studies on Hysteria, prior to Bion it had lost its independent significance and role in psychotherapeutic theories. We would contend that even if the concept reverie has become increasingly popular in recent psychotherapeutic discourse, the relative neglect of its history and philosophy have led to problematic ways of implementing the concept in both the theory and practice of psychotherapy. We start from Jean-Jacques Rousseau, moving on to Freud, William James, Henri Bergson and Gaston Bachelard. We present our view of why Bion considered reverie to be an indispensable tool in explicating certain psychoanalytic dimensions. We also reveal the kinds of historical and philosophical commitments that are embedded in the concept of reverie and append brief comments on the relevance of our analysis to the present state of psychotherapy and psychotherapy research.