Catechism of the Catholic Church §1557 — excerpt
The Second Vatican Council "teaches . . that the fullness of the sacrament of Holy Orders is conferred by episcopal consecration, that fullness namely which, both in the liturgical tradition of the Church and the language of the Fathers of the Church, is called the high priesthood, the acme (summa) of the sacred ministry."
This translation is under copyright, so only the cited words are quoted here. Follow the link for the full text. Translation: English translation of the Catechism of the Catholic Church, 2nd ed. (Libreria Editrice Vaticana), as posted at vatican.va.
Also cites: LG 21 # 2