Euthydemus (Ancient Greek: Εὐθύδημος) may refer to:

• Euthydemus, a fleet commander for Athens during the Sicilian Expedition, 415 to 413 BC
• Euthydemus of Chios, a 5th-century sophist who features in Plato's Euthydemus
• Euthydemus, a son of Cephalus, mentioned in Plato's Republic
• Euthydemus, a son of Diocles, mentioned in Xenophon's Memorabilia
• Euthydemus I (3rd century BC), ruler of the Greco-Bactrian Kingdom
• Euthydemus II (2nd century BC), ruler of the Greco-Bactrian Kingdom
• Euthydemus (tyrant) (3rd century BC), tyrant of Sicyon

• Euthydemus (dialogue), a dialogue by Plato