Erasistratus of Ceos was a Greek physician and anatomist active in the first half of the 3rd century BCE, around 250 BCE. A student of Theophrastus in Athens, he later moved to Alexandria, where he served at the royal court and founded his own influential medical school. According to later historians, a famous story claims he diagnosed a prince's love-sickness, illustrating his renown.

He is considered a founder of systematic human anatomy. In Alexandria, he conducted detailed dissections of human bodies, a rare practice at the time. His investigations led to major discoveries: he distinguished the brain's cerebrum and cerebellum, described its folds, and identified sensory and motor nerves. He also produced advanced studies of the heart and blood vessels.

None of Erasistratus's own writings survive intact. His ideas are known only through fragments and reports by later medical authors like Galen. His lost works included titles such as On Fevers, On Paralysis, and a major theoretical text called General Principles.

Modern scholars regard Erasistratus as a pivotal figure in the history of science. His empirical approach to dissection set a new standard for anatomical knowledge. While his physiological theories, which explained the body using a system of vessels carrying "vital spirit," were later rejected, his anatomical observations remained foundational. His school rivaled that of Herophilus in Alexandria for centuries, and his emphasis on diet and mechanical causes for disease influenced more rationalist medical traditions.