Dia (Ancient Greek: Δία or Δῖα, "heavenly", "divine" or "she who belongs to Zeus"), in ancient Greek religion and folklore, may refer to:

• Dia, a goddess venerated at Phlius and Sicyon. She was seen by the locals as identical to Hebe and/or Ganymeda.^[1][2]
• Dia, daughter of Aeolus, keeper of the winds and Telepora or Telepatra, daughter of Laestrygon. She was the sister of Androcles, Chrysippus, Iocastus, Phalacrus, Pheraemon, Xuthus, and the daughters' as Aeole, Astycrateia, Hephaestia, Iphthe and Periboea.^[3]
• Dia, daughter of King Porthaon of Calydon^[4] and mother of Thersites and possibly the remaining five sons by Agrius.^[5]
• Dia, daughter of the king Lycaon (thus sister of Callisto), mother of Dryops by Apollo.^[6][7] She concealed her new-born infant in a hollow oak tree.^[8]
• Dia, second wife of the Thracian king Phineus and by him, mother of Mariandynus and Thynus. She falsely accused of rape her step sons, Parthenius and Crambis, leading to their blindness and eventual imprisonment by Phineus.^[9]
• Dia, the Perrhaebian daughter of Deioneus^[10] or Eioneus,^[11][12] wife of Ixion^[13] (who killed her father so as to not pay the bride price) and with her husband, she became mother of the Lapith Pirithous, whose marriage to Hippodameia was the occasion of the Lapiths' battle with the Centaurs. According to Homer, after having sex with Zeus, who was disguised as a stallion, she gave birth to Pirithous; a folk etymology derived Pirithous' name from peritheein (περιθεῖν "to run around"), because that was what Zeus did to seduce Dia.^{[14][15][16][17][18][19]} The Jovian moon Dia is named after this Dia.^[20]
• Dia, alternate name for Hippodamia, the wife of Pirithous (thus daughter-in-law of another Dia).^[21]
• Dia, mother of Pittheus by Pelops.^[22] She may have been identical with another Hippodamia, daughter of Oenomaus.

In ancient Roman religion, Dia may refer to Dea Dia.