Eileithyia or Ilithyia (/ɪlɪˈθaɪ.ə/; Ancient Greek: Εἰλείθυια; Ἐλεύθυια (Eleuthyia) in Crete, also Ἐλευθία (Eleuthia) or Ἐλυσία (Elysia) in Laconia and Messene, and Ἐλευθώ (Eleuthō) in literature) was the Greek goddess of childbirth and midwifery, and the daughter of Zeus and Hera. In the cave of Amnisos (Crete) she was related with the annual birth of the divine child, and her cult is connected with Enesidaon (the earth shaker), who was the chthonic aspect of the god Poseidon. It is possible that her cult is related with the cult of Eleusis. In his Seventh Nemean Ode, Pindar refers to her as the maid to or seated beside the Moirai (Fates) and responsible for the creation of offspring. Her son was Sosipolis, who was worshiped at Elis.

The earliest form of the name is the Mycenaean Greek 𐀁𐀩𐀄𐀴𐀊, e-re-u-ti-ja, written in the Linear B syllabic script. Ilithyia is the latinisation of Εἰλείθυια.

The etymology of the name is uncertain, and debated among scholars. R. S. P. Beekes suggests a non-Indo-European etymology, and Nilsson believed that the name is Pre-Greek. 19th-century scholars suggested that the name is Greek, derived from the verb eleutho (ἐλεύθω), "to bring", the goddess thus meaning The Bringer. Walter Burkert believed that Eileithyia is the Greek goddess of birth and that her name is pure Greek. However, the relation with the Greek prefix ἐλεύθ is uncertain, because the prefix appears in some pre-Greek toponyms like Ἐλευθέρνα (Eleutherna); therefore it is possible that the name is pre-Greek. Her name Ἐλυσία (Elysia) in Laconia and Messene probably relates her with the month Eleusinios and Eleusis. Nilsson also believed that the name "Eleusis" is pre-Greek.

According to F. Willets, the goddess shows a clear connection to a preexisting Minoan goddess, as well as an earlier Neolithic concept. Eileithyia's guidance in childbirth may give influence of the first midwife. To Homer, she is "the goddess of childbirth". The Iliad pictures Eileithyia alone, or sometimes multiplied, as the Eileithyiai:

And even as when the sharp dart striketh a woman in travail, [270] the piercing dart that the Eilithyiae, the goddesses of childbirth, send—even the daughters of Hera that have in their keeping bitter pangs;

— Iliad 11.269–272

Hesiod (c. 700 BC) described Eileithyia as a daughter of Hera by Zeus (Theogony 921)—and the Bibliotheca (Roman-era) and Diodorus Siculus (c. 90–27 BC) (5.72.5) agreed. Also, a poem at the Greek Anthology Book 6, mention Eileithyia as Hera's daughter. But Pausanias, writing in the 2nd century AD, reported another early source (now lost): "The Lycian Olen, an earlier poet, who composed for the Delians, among other hymns, one to Eileithyia, styles her as 'the clever spinner', clearly identifying her with the Fates, thus making her older than Cronus." Being the youngest born to Gaia, Cronus was a Titan of the first generation and he was identified as the father of Zeus. Likewise, the meticulously accurate mythographer Pindar (522–443 BC) also makes no mention of Zeus:

Eleithuia, seated beside the deep-thinking Fates, hear me, creator of offspring, child of Hera great in strength.