In Greek mythology, Iphianassa is an obscure and controversial daughter of Agamemnon, sometimes considered identical to Iphigeneia. Iphianassa, "strong queen", is also one of the names of the consort of Endymion and one of the three maenadic daughters of Argive Proetus by Stheneboea who were purified of their madness by Melampus.
Extant plays by Sophocles, Aeschylus and Euripides on the tale of Orestes and Electra do not include her as a character. This is consistent with the theory that she and Iphigeneia are one and the same. On the other hand, Sophocles does mention her, and hints that she lives in the palace of Aegisthus and Clytemnestra, together with Electra and Chrysothemis.
Lucretius, in De Rerum Natura, mentions Iphianassa being sacrificed by her father on the altar of Diana (Artemis) at Aulis as an offering to ensure a successful voyage, in undoubted reference to the tradition of Iphigeneia. Lucretius cited this episode to make the point: "Superstition was able to induce so great an evil."