In Greek mythology, Clytemnestra (, UK also ; Ancient Greek: Κλυταιμνήστρα, romanized: Klutaimnḗstra, pronounced [klytai̯mnɛ̌ːstraː]), was the wife of Agamemnon, king of Mycenae, and the half-sister of Helen of Troy. With Agamemnon, she was the mother of Orestes and Electra.

Clytemnestra appears as a character in multiple ancient Greek works, including the Homeric epics and plays by Aeschylus, Sophocles, and Euripides. She is infamous for murdering Agamemnon and the Trojan princess Cassandra, whom Agamemnon had taken as a war prize, when they returned from Trojan War. However, in Homer's Odyssey and Iliad, her role in Agamemnon's death is unclear and her character is significantly more subdued.