Book 5 describes the way of life of the guardians. Polemarchus asks Socrates to explain the concept that wives and children should be held in common. Socrates says that females have the say ability to rule as males, so there will be female guardians, educated in the same way and expected to perform the same duties as the men.

Socrates goes on to describe the family structure of the guardians. Traditional families will be abolished, Socrates says, because they lead to divisiveness and conflict within the city. Instead, guardians will only be permitted to have sex during special festivals, held several times a year, and their partners will be secretly decided by the state. Children born during the festivals are raised in a group family, so in a sense they are all brothers and sisters to each other. In this way, the whole city becomes one family, effectively short-circuiting internal strife.

Socrates concludes by asserting that both male and female guardians will fight to defend the city against outsiders. Wars against fellow Greeks should be conducted in such a way as to minimize damage.