Catechism of the Catholic Church §1556 — excerpt
To fulfil their exalted mission, "the apostles were endowed by Christ with a special outpouring of the Holy Spirit coming upon them, and by the imposition of hands they passed on to their auxiliaries the gift of the Spirit, which is transmitted down to our day through episcopal consecration."
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.
Whole chapters cited: Acts 24
Also cites: LG 21