This paper has two parts. First, I examine Basil of Caesarea’s theological anthropology and show how he understands the human being as a body-soul unity. The body is the good instrument of the soul. It is marvelous because it has been molded by God’s own hands. In the second part, I examine what I call Basil’s theological physiology, which flows naturally from his anthropology. Because the human body is good and great, he recommends the scientific study of its structures. In his sermons, he uses his knowledge of physiology and medicine to make illustrations and to support Christian practices such as fasting. All in all, he brings various sources of knowledge together to offer his congregation an edifying and informed theological interpretation of the human body.