The Scientific Revolution saw the redefinition of many scholastic notions about the nature of the world and its constituent parts, from planets to particles. Wang’s book introduces a convincing and wide-ranging narrative of the changing place of ‘occult qualities’ in the context of emergent new scientific methods and early modern disciplinary realignments. Through in-depth analysis of the diverse treatments of this notion, whereby it becomes now a hollow phrase, now a touchstone for the superiority of new physics, Wang shows how the transformation of this notion is key to understanding almost every facet of the new physics of the age.