An oracle is a person or agency considered to be a source of wise counsel or prophetic opinion; an infallible authority, usually spiritual in nature. It can also be a prediction of the future, from the gods, that is spoken through another object or life-form. In the ancient world many sites gained a reputation for the dispensing of oracular wisdom: they too became known as "oracles", as did the oracular utterances themselves, whose very name is derived from the Latin verb orare, to speak.

Oracles were common in many civilizations of antiquity. In China, the use of oracle bones dates as far back as the Shang Dynasty, (1600 BC - 1046 BC). The I Ching, or "Book of Changes", is a collection of linear signs used as oracles that dates from that period. Although divination with the I Ching is thought to have originated prior to the Shang Dynasty, it was not until King Wu of Zhou (1046 BC-1043 BC) that it took its present form. In addition to its oracular power, the I Ching has had a major influence on the philosophy, literature and statecraft of China from the time of the Zhou Dynasty (1122 BC - 256 BC).

In classical Greece, the pre-eminent oracle — the Sibyl (or Pythia) — operated at the temple of Apollo at Delphi. This oracle exerted considerable influence throughout Hellenic culture; the Greeks consulted her prior to all major undertakings: wars, the founding of colonies, and so forth. The semi-Hellenic countries around the Greek world, such as Lydia, Caria, and even Egypt also respected her. Croesus of Lydia consulted Delphi before attacking Persia, and according to Herodotus was told, "If you do, you will destroy a great empire." Believing the response favorable, Croesus attacked, but it was his own empire that was ultimately destroyed by the Persians.