(Latin: “power of a father”), in Roman family law, power that the male head of a family exercised over his children and his more remote descendants in the male line, whatever their age, as well as over those brought into the family by adoption. This power meant originally not only that he had control over the persons of his children, amounting even to a right to inflict capital punishment, but that he alone had any rights in private law. Thus, acquisitions of a child became the property of the father. The father might allow a child (as he might a slave) certain property to treat as his own, but in the eye of the law it continued to belong to the father.

Patria potestas ceased normally only with the death of the father; but the father might voluntarily free the child by emancipation, and a daughter ceased to be under the father's potestas if upon her marriage she came under her husband's manus (q.v.), a corresponding power of husband over wife.

By classical times, the father's power of life and death had shrunk to that of light punishment, and sons could keep as their own what they earned as soldiers (peculium castrense). By Justinian's day (527–565), the rules of peculium castrense were extended to many sorts of professional earnings; and in other acquisitions, such as property inherited from the mother, the father's rights were reduced to a life interest.