In this article, I claim that the treatise known as περὶ πνεύματος/De spiritu (481a-486b Bekker) was written by Theophrastus. My overall argument unfolds in three stages: first, I briefly summarize the arguments against De spiritu’s authenticity in Aristotle’s corpus. This summary will lead to my first argument which uses the very same reasons that prove the non-Aristotelian authorship to claim the Theophrastean one, in particular linguistic aspects of the text (§2). Next, I will focus on chronology, by discussing the mention (...) of one Aristogenes to show that Aristotle could not have known this individual (§3). Third and last, I will examine various aspects of the work that demonstrate stylistic and argumentative connections (§4), as well as doctrinal affinities with the works of Theophrastus, although some have attributed it to Strato (§5). On the basis of these arguments, I conclude that the weight of the evidence makes On Breath a work by Theophrastus (or his circle) rather than one composed by Aristotle. (shrink)