Ostracism was a well-established practice used in classical Greece during the fifth century b.c.e. to banish public figures from the city. Created by Cleisthenes, it was used in Athens for the expulsion of Hipparchos in 488–487 b.c.e.

Ostracism represented a ritual and symbolic course of action. Far from being a judicial mechanism (no debate or speeches were allowed), ostracism was an effective weapon to attack public individuals who may have gained too much power.

The threat of ostracism was also effective at dissolving open confrontations between enemy parties. However, only a few instances of successful ostracisms have been attested, in most cases against prominent citizens from propertied families, and its actual uses were infrequent.

Each year, during the sixth prytany of the assembly, the people decided through a preliminary vote whether an ostrakophoria should be organized that year. If they agreed on that, during the eight prytany—that is, two months after the decision—the polling itself took place in the marketplace (agora). During that meeting, each citizen marked a potshard (ostrakon) with the name of a person he wished to see expelled from the polis and put it into an urn.

No list of candidates was drafted before the election. The man whose name was scratched on the most ostraka was exiled from Athens for 10 years, but there is controversy on the number of votes needed for this result: For some specialists a quorum of 6,000 votes was required for the procedure to have effect, while others believe that a person had to be identified in at least 6,000 votes in order to be ostracized.

Thousands of ostraka have been found in different excavations, especially in the Kerameikos and the Athenian agora. Many of them were found bearing the same name (for example, Themistokles) and were apparently written by the same hand and were carefully painted.

It is possible that during the two months separating the first decision and the voting, a number of public campaigns were held in order to convince people on the need of ousting a certain person and that prepared ostraka were distributed among voters.

Contrary to legal punishments ostracism had rather mild consequences. It did not imply confiscation or loss of civic status, and in many cases evidence shows that ostracized individuals, like Kimon or Aristeides, were recalled to the city before the 10-year period had expired.

The last ostracism in Athens was probably held in 416–415 b.c.e., when the demagogue Hyperbolos wanted to banish Alkibiades or Nikias from the city.

Threatened by the possibility of being expelled, the two politicians managed to get rid of their common enemy, and Hyperbolos himself was ostracized. Sources indicate that the Athenian people were disgusted by the situation and that the procedure of ostracism was not implemented again.

The truth is that new legal mechanisms capable of dealing with the possibility of removing undesirable politicians through lawsuits, such as the graphe paranomon, were put into place by this time and helped to address these issues in less unpredictable manners.

Other Greek cities such as Argos, Megara, and Miletos implemented the process of ostracism as well. In Syracuse, it was called petalismos, because names were written in olive trees.