In Greek mythology, Amalthea ("tender") is the foster-mother of Zeus. She is sometimes represented as the goat which suckled the infant-god in a cave in Crete, sometimes as a nymph of uncertain parentage (daughter of Oceanus, Haemonius, Olen, Melisseus), who brought him up on the milk of a goat. This goat having broken off one of its horns, Amalthea filled it with flowers and fruits and presented it to Zeus, who placed it together with the goat amongst the stars. According to another story, Zeus himself broke off the horn and gave it to Amalthea, promising that it would supply whatever she desired in abundance. Amalthea gave it to Achelous (her reputed brother), who exchanged it for his own horn which had been broken off in his contest with Heracles for the possession of Deianeira. According to ancient mythology, the owners of the horn were many and various. Speaking generally, it was regarded as the symbol of inexhaustible riches and plenty, and became the attribute of various divinities (Hades, Gaea, Demeter, Cybele, Hermes), and of rivers (the Nile) as fertilizers of the land. See: Cornucopia and Horn of plenty. The term "horn of Amalthea" is applied to a fertile district, and an estate belonging to Titus Pomponius Atticus was called Amaltheum. Cretan coins represent the infant Zeus being suckled by the goat; other Greek coins exhibit him suspended from its teats or carried in the arms of a nymph (Ovid, Fasti, v. 115; Metam. ix. 87).

Her skin also became the aegis in some traditions.