The play is set in the Greek military camp at Aulis in front of the tent of Agamemnon, king of Mycenae and commander of the expedition. It is the middle of the night. Agamemnon summons the Old Man, a faithful enslaved man who was part of the dowry Agamemnon received when he married his wife Clytemnestra. In the dialogue between the two men, the Old Man points out that it is late and asks Agamemnon why he is not sleeping like everybody else. Agamemnon says that he envies those who are not burdened by power and honor, prompting the Old Man to remind him of the “glory” (20) that such burdens bring. In a short speech, the Old Man tells Agamemnon that such complaints are improper for a king and that all mortals must experience unhappiness and suffering sometimes. He then asks Agamemnon about the letter that he sees him writing and rewriting.

Agamemnon provides the play’s exposition. He describes the daughters of Leda and Tyndareus. One of these daughters, Clytemnestra, is his wife. Another is Helen, who had many powerful suitors because of her famed beauty. Tyndareus feared that if he chose one of the suitors as Helen’s husband the rest would turn against him, so he made all the suitors swear an oath: