The Pneumatist school of medicine has the distinction of being the only medical school in antiquity named for a belief in a part of a human being. Unlike the Herophileans or the Asclepiadeans, their name does not pick out the founder of the school. Unlike the Dogmatists, Empiricists, or Methodists, their name does not pick out a specific approach to medicine. Instead, the name picks out a belief: the fact that pneuma is of paramount importance, both for explaining health and disease, and for determining treatments for the healthy and sick. In this paper, we re-examine what our sources say about the pneuma of the Pneumatists in order to understand what these physicians thought it was and how it shaped their views on physiology, diagnosis and treatment.