The ephors (Classical Greek Ἔφορος) (from the Greek ἐπί epi, "on" or "over", and ὁράω horaō, "to see", i.e. "one who oversees") were leaders of ancient Sparta and shared power with the Spartan kings. Five ephors were elected annually, who "swore on behalf of the city", while the kings swore for themselves.

Herodotus claimed that the institution was created by Lycurgus, while Plutarch considers it a later institution. It may have arisen from the need for governors while the kings were leading armies in battle. The ephors were elected by the popular assembly, and all citizens were eligible for election. They were forbidden to be reelected. They provided a balance for the two kings, who rarely cooperated with each other. Plato called them tyrants who ran Sparta as despots, while the kings were little more than generals.

According to Plutarch, every autumn, at the crypteia, the ephors would pro forma declare war on the helot population so that any Spartan citizen could kill a helot without fear of blood guilt.