Erasistratus (; Ancient Greek: Ἐρασίστρατος; c. 304 – c. 250 BC) was a Greek anatomist and royal physician under Seleucus I Nicator of Syria. Along with fellow physician Herophilus, he founded a school of anatomy in Alexandria, where they carried out anatomical research. As well, he is credited with helping to found the methodic school of teachings of medicine in Alexandria whilst opposing traditional humoral theories of Hippocratic ideologies. Together with Herophilus, he is credited by historians as the potential founder of neuroscience due to his acknowledgements of nerves and their roles in motor control through the brain and skeletal muscles.
Furthermore, Erasistratus is seen as one of the first physicians/scientists to conduct recorded dissections and potential vivisections alongside Herophilus. The two physicians were said by several Roman authors, notably Augustine, Celsus, and Tertullian, to have performed controversial vivisections on criminals to study the anatomy and possible physiology of human organs while they were in Alexandria. Because of their research, Erasistratus and Herophilus were heavily criticized for their utilization of vivisections; specifically, by the author Tertullian who followed Christian values. Erasistratus and Herophilus are thought to be the only physicians to perform systematic dissections on the human body until the Renaissance.