The first book to show how the concept of bodily organs emerged and how ancient tools influenced conceptualizations of human anatomy and its operations. Medicine is itself a type of technology, involving therapeutic tools and substances, and so one can write the history of medicine as the application of different technologies to the human body. In Tools and the Organism, Colin Webster argues that, throughout antiquity, these tools were crucial to broader theoretical shifts. Notions changed about what type of object a body is, what substances constitute its essential nature, and how its parts interact. By following these changes and taking the question of technology into the heart of Greek and Roman medicine, Webster reveals how the body was first conceptualized as an “organism”—a functional object whose inner parts were tools, or organa, that each completed certain vital tasks. He also shows how different medical tools created different bodies. Webster’s approach provides both an overarching survey of the ways that technologies impacted notions of corporeality and corporeal behaviors and, at the same time, stays attentive to the specific material details of ancient tools and how they informed assumptions about somatic structures, substances, and inner processes. For example, by turning to developments in water-delivery technologies and pneumatic tools, we see how these changing material realities altered theories of the vascular system and respiration across Classical antiquity. Tools and the Organism makes the compelling case for why telling the history of ancient Greco-Roman medical theories, from the Hippocratics to Galen, should pay close attention to the question of technology.