Metrodorus of Chios was a Greek philosopher who lived during the 4th century BCE. He was a native of the island of Chios and studied under the atomist thinker Democritus. He is also recorded as having taught Anaxarchus, who would later influence skeptical philosophy.

Metrodorus wrote several works, but they survive only in fragments quoted by later authors. His writings included a major treatise On Nature, which explored atomist physics, and a now-lost Trojan History, showing his interest beyond pure philosophy.

His historical importance lies in his role as a bridge between earlier atomism and later philosophical movements. He extended the ideas of Democritus, proposing, for example, that there are countless worlds in different stages of existence. More strikingly, he expressed radical doubt about the possibility of knowledge. According to modern scholars, a famous opening statement attributed to him questioned whether we can know anything at all—even whether knowing is possible. This extreme skepticism positions him as a significant forerunner to the later traditions of philosophical skepticism.