Praxagoras of Cos was a Greek historian of the 4th century BCE, a native of the island of Cos in the southeastern Aegean. Beyond his name, origin, and profession, no specific biographical details survive.

His sole attested work is a history of Athens, now lost and preserved only in fragments. It was composed in the Ionic dialect.

Praxagoras is significant as an early Atthidographer, a local historian of Athens. His work is cited by later authors like Plutarch, who used it as a source for his Life of Theseus. Alongside other Atthidographers, he helped preserve Athenian traditions and constitutional history, influencing broader historical narratives.