Stated in the Catholic Churche Canon Law: 

Can. 1008ⁿ By divine institution, some of the Christian faithful are marked with an indelible character and constituted as sacred ministers by the sacrament of holy orders. They are thus consecrated and deputed so that, each according to his own grade, they may serve the People of God by a new and specific title.

Can. 1009: 

§1. The orders are the episcopate, the presbyterate, and the diaconate.

§2. They are conferred by the imposition of hands and the consecratory prayer which the liturgical books prescribe for the individual grades.

§3. Those who are constituted in the order of the episcopate or the presbyterate receive the mission and capacity to act in the person of Christ the Head, whereas deacons are empowered to serve the People of God in the ministries of the liturgy, the word and charity