Nessos of Chios was a philosopher who lived in Greece during the 5th century BCE, in the Classical period. He is identified as a Presocratic thinker, a group concerned with the fundamental nature of the world. His primary historical role was as a teacher of the much more famous philosopher Democritus.

No specific details about his life, background, or education survive. He is mentioned only in connection to his student. According to the ancient biographer Diogenes Laertius, Democritus once referred to Nessos with a cryptic term meaning "shore-fighter." The exact meaning is unclear, but some scholars suggest it might imply Nessos was a sophist or skilled in rhetorical debate.

No works written by Nessos himself are known to have survived, and no titles or contents are recorded in ancient sources. His entire significance comes from his association with Democritus, who would go on to develop the influential atomic theory of matter. This connection places Nessos within the network of early Greek natural philosophy, representing a link in the transmission of these ideas, even if his own contributions are lost to history.