In Greek mythology, Ceto (; Ancient Greek: Κητώ, romanized: Kētṓ, lit. 'sea monster' or 'whale') may refer to three divine women:
Ceto, a primordial sea goddess and daughter of Pontus (Sea) and Gaia (Earth). She was the mother of the Phorcydes by her brother Phorcys.
Ceto, a "naiad daughter of Oceanus" and thus one of the Oceanids. Her mother was probably the Titaness Tethys. Ceto bore Helios a daughter, Astris.
Ceto, the Nereid of sea-monsters and one of the 50 sea nymph daughters of the "Old Man of the Sea" Nereus and the Oceanid Doris.