This dissertation focuses on the issue of two Ancient Greek institutions, friendship (xenia) and supplication (hikesia), in the tragedies of Aeschylus and Sophocles. I highlight their interconnectedness and difference, as well as the ethical dilemma to which these two institutions give rise. I argue from historical proofs of the two institutions. Both xenia and hikesia are related to the principle of reciprocity, which in turn is grounded on more primitive cultural concepts among the ancient Indo-Europeans, such as the concept of gift and exchange. In the Greek world, xenia and hikesia are often linked so that suppliants usually form friendship with their host. But in other cases, for example in Aeschylus's Suppliants, the suppliants become disruptive and murderous towards their host. In thinking about how the suppliant or the guest can live peacefully with their host, I introduce ancient Confucian teaching of reciprocal and mutual respect and empathy. By citing a non-western source, I would like to demonstrate how the principle of reciprocity extends beyond ancient Greeks and Romans and is shared by a larger portion of the humanity. In my study, I selected three tragedies from Aeschylus and Sophocles that represent three crucial aspects of the discussion. In Oedipus at Colonus, the supplication of Oedipus eventually turns into good xenia, by which a permanent bond between the suppliant's native city, Thebes, and the host city, Athens. In Philoctetes, the xenia between Philoctetes and the visitors is marred by Odysseus's use of deceit. The friendship is finally concluded when Neoptolemus breaks his alliance with Odysseus and offers help in order to rescue Philoctetes from his exile. In Suppliants, the Danaids who are fleeing forced marriage in Egypt arrive at Argos and request to be admitted. However, their supplication is contested by Pelasgus, king of Argos. The Danaids have to blackmail the king so that their supplication request can be accepted, which will later trigger the war between Argos and the Danaids's persecutors, leading to the death of King Pelasgus and the downfall of his kingdom.