A cleruchy (Greek: κληρουχία, klēroukhia) in Classical Greece, was a specialized type of colony established by Athens. The term comes from the Greek word κληροῦχος, klērouchos, literally "lot-holder".

Normally, Greek colonies were politically independent; they would have a special relationship with the mother city the metropolis but would otherwise be independent entities. Cleruchies were significantly different. The settlers or cleruchs would retain their Athenian citizenship, and the community remained a political dependency of Athens.

Cleruchies were established as a means of exporting excess and generally impoverished populations to conveniently distant localities, such as the Thracian Chersonese on the far side of the Aegean Sea. Under the cleruchy arrangement, the participating citizen received a plot (or kleros) of agricultural land, hence a means to earn his livelihood. This elevated the citizen to the property class of zeugitai. The cleruch would be obliged to defend his colony by serving it as a hoplite.

This arrangement benefited Athens in three principal ways:

  • It reduced population pressure in Athens itself;
  • It increased Athenian military power, as the cleruchs formed military garrisons;
  • It increased the economic power of Athens, as it enabled more of its citizens to become property holders.

The first known cleruchy is thought to have been Salamis, captured by Athens from Megara in the 6th century BC. Other cleruchies were established on the Thracian Chersonese following its recapture from the Persian Empire after the Greco-Persian Wars of the 5th century BC, and at Chalcis following that city's defeat in a war with Athens. During the period of the Delian League and the Second Athenian League (5th–4th century BC), many more cleruchies were created by Athens such as on Samos Island proved worthy in the Social War.