AbstractIn this paper I argue that William Harvey believed in a form of astrology. It has long been known that Harvey employed a macrocosm–microcosm analogy and used alchemical terminology in describing how the two types of blood change into one another. This paper then seeks to examine a further aspect of Harvey in relation to the magical tradition. There is an important corollary to this line of thought, however. This is that while Harvey does have a belief in astrology, it is strongly related to Aristotle's views in this area and is quite restricted and attenuated relative to some contemporary beliefs in astrology. This suggests a more general thesis. While Harvey was amenable to ideas which we associate with the natural magic tradition, those ideas had a very broad range of formulation and there was a limit to how far he would accept them. This limit was largely determined by Harvey's adherence to Aristotle's natural philosophy and his Christian beliefs. I argue that this is also the case in relation to Harvey's use of the macrocosm–microcosm analogy and of alchemical terminology, and, as far as we can rely on the evidence, this informs his attitudes towards witches as well. Understanding Harvey's influences and motives here is important in placing him properly in the context of early seventeenth-century thought.