The power held by the pater familias was called patria potestas, "paternal power." Under the laws of the Twelve Tables, the pater familias had vitae necisque potestas --- the "power of life and death" --- over his children, his wife, and his slaves, all of whom were said to be sub manu, "under his hand." For a slave to become a freedman, he would have to be delivered "out of the hand" of the pater familias, hence the terms manumissio and emancipatio. At law, at any rate, his word was absolute and final. If a child was unwanted, under the Roman Republic the pater familias had the power to order the child put to death by exposure.
He had the power to sell his children into slavery; Roman law provided, however, that if a child has been sold as a slave three times, he is no longer subject to the patria potestas. The pater familias has the power to approve or reject marriages of his sons and daughters; however, an edict of the Emperor Augustus provided that the pater familias could not withhold that permission lightly.
Only a Roman citizen could enjoy the status of pater familias. There could only be one holder of the office within a household. Even male adult children remained under the authority of their fathers while he still lived, and could not acquire the rights of a pater familias while he was yet alive; at least in legal theory, all their property was acquired on behalf of their fathers, and he, not they, had ultimate authority to dispose of it. Those who lived in their own households at the time of the father's death succeeded to the status of pater familias over their respective households.
Over time, the absolute authority of the pater familias tended to be weakened, and rights that theoretically existed were no longer enforced or insisted upon.