This chapter tells the story of the discovery of the circulation by William Harvey. However, it starts with Galen in Greece, the reigning expert on the circulation until Harvey. We encounter the details of Galen’s concept of physiology; namely that “food is transformed into blood in some central organ, and that the blood then moves slowly outward to be assimilated and ultimately lost through invisible emanation.” We meet early thinkers who in part contested Galen in the thirteenth century and later, before Harvey. We see the critical and innovative “experimental” approach of Harvey’s work, providing compelling evidence to his conclusions.