Since the beginning, the ordained ministry has been conferred and exercised in three degrees: that of bishops, that of presbyters, and that of deacons. The ministries conferred by ordination are irreplaceable for the organic structure of the Church: without the bishop, presbyters, and deacons, one cannot speak of the Church. (CCC 1593)
In the Latin Church the sacrament of Holy Orders for the presbyterate is normally conferred only on candidates who are ready to embrace celibacy freely and who publicly manifest their intention of staying celibate for the love of God's kingdom and the service of men. (CCC 1599)