Krypteria or Crypteia was a kind of secret police force organised by the ruling classes of Sparta and targeted at the enslaved Helot population that economically supported it.

Young Spartan men who had completed their training at the agoge with such success that they were marked out as potential future leaders, would be given the opportunity to test their skills and prove themselves worthy of the Spartan military tradition through membership of the Crypteia.

Every autumn, the Spartan Ephors would declare war on the Helot population so that any Spartan citizen could kill a Helot without fear of blood guilt. Armed only with dagger, the Crypteria were sent out into the countryside with the instructions to kill any Helot they encountered at night and to take any food they needed. This could be used to remove any Helots considered troublesome and provide the young men with a manhood test and experience of their first kill. Such brutal oppression of the Helots permitted the Spartans to control the agrarian population and devote themselves to military practice. It may also have contributed to the Spartans' reputation for stealth.

Both Aristotle and Plutarch describe the Crypteia.