Catechism of the Catholic Church §1287 — excerpt
This fullness of the Spirit was not to remain uniquely the Messiah's, but was to be communicated to the whole messianic people. On several occasions Christ promised this outpouring of the Spirit, a promise which he fulfilled first on Easter Sunday and then more strikingly at Pentecost.
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.