The Oracle of Delphi was one of the most famous elements of Ancient Greece. Even though consulting the Oracle was time-consuming and the results questionable at best, the Oracle was widely believed to have knowledge beyond that possessed by mere mortals.

The Oracle was the focal point of Delphi, one of Greece's more famous city-states. The idea was that the Oracle was speaking on behalf of the god Apollo. The focal point of the Oracle was the Pythia, an older woman who kept to herself in a hidden chamber, called the inner sanctum. In this inner chamber was a chasm, up through which spewed vapors. The Oracle would sit on a tripod above the chasm and inhale the vapors. Some traditions say that the Pythia also chewed on laurel leaves. Then, the Oracle, in a trance, would speak to a group of attending priestesses, who would interpret the words and then speak the pronouncements in words that could be understood by those consulting the Oracle.

The pronouncements of the Oracle were often not straightforward. Many were open to interpretation. Many had more than one meaning.

Among the famous pronouncements of the Oracle (as interpreted by priestesses):

• Croesus, King of Lydia, was considering an attack on the Persians. The Oracle prophesied that his attack would result in the downfall of a great empire. Croesus carried out the attack, and a great empire did fall; however, it was his empire that fall, as the Persians won a vicious victory.
• Athens, in desperation during the Persian Wars, consulted the Oracle. The result was a prophecy that wooden walls would save Athens. The Athenian general Themistocles interpreted this as his city-state's need for a strong navy; the Greek naval victory at the Battle of Salamis was the result.
• Philip II of Macedon was told that with silver spears, he could conquer the world. He interpreted this as a need to control the silver mines in Illyria and Thrace and was successful at doing so.
• Philip was also told that whoever could rise his "unridable" horse would conquer the world; this prophecy came true, to a degree, in that Philip's son Alexander tamed the horse, Bucephalus, and then rode that steed to victory in conquering the known world.
• The Roman emperor Nero was told that the number 73 would mark his downfall. He was 30 when he heard this and so thought that he would reign for a long time; however, a 73-year-old man named Galba led a revolt that resulted in Nero's death.

The nearby Castalian Spring played a large part in the proceedings. The Pythia and priestesses would was themselves in the spring before a pronouncement. Those who consulted the Oracle would also drink from the spring, as part of the ritual.

People who came to Delphi to consult the Oracle brought gifts. Delphi thus had several treasuries in which these gifts were stored.