Catechism of the Catholic Church: 1536; 1597; 1598-1599
ARTICLE 6 THE SACRAMENT OF HOLY ORDERS

1536  Holy Orders is the sacrament through which the mission entrusted by Christ to his apostles continues to be exercised in the Church until the end of time: thus it is the sacrament of apostolic ministry. It includes three degrees: episcopate, presbyterate, and diaconate.
1597  The sacrament of Holy Orders is conferred by the laying on of hands followed by a solemn prayer of consecration asking God to grant the ordinand the graces of the Holy Spirit required for his ministry. Ordination imprints an indelible sacramental character.

Who Can Receive This Sacrament?
1598  The Church confers the sacrament of Holy Orders only on baptized men (viri), whose suitability for the exercise of the ministry has been duly recognized. Church authority alone has the responsibility and right to call someone to receive the sacrament of Holy Orders.
1599  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.