The Oracle of Ammon in the oasis of Siwa in Libya, northwest of Egypt, was an oracle of the god Ammon (Greek Zeus-Amon) founded by people from Thebes (Egypt). The way in which the god was represented in Siwa and in Thebes was the same.

The Greeks of Greece learned about the oracle through the Greeks of Cyrene, and Sparta was the first city to connect with it, followed by Thebes, Olympia, Dodona, Elis and others. The Athenians also sent some inquiries there. Some temples of Zeus Ammon were erected in various parts of Greece.

The revelations were given by a number of people, apparently quite large (there is even talk of eighty). In Strabo's time the oracle was quite neglected and in decay.