Catechism of the Catholic Church: Purgatory

From the Catechism of the Catholic Church:

1030 All who die in God's grace and friendship, but still imperfectly purified, are indeed assured of their eternal salvation; but after death they undergo purification, so as to achieve the holiness necessary to enter the joy of heaven.

1031 The Church gives the name Purgatory to this final purification of the elect, which is entirely different from the punishment of the damned. The Church formulated her doctrine of faith on Purgatory especially at the Councils of Florence and Trent. The tradition of the Church, by reference to certain texts of Scripture, speaks of a cleansing fire (1 Cor 3:15; 1 Pet 1:7)...

1032 This teaching is also based on the practice of prayer for the dead, already mentioned in Sacred Scripture: "Therefore (Judas Maccabeus) made atonement for the dead, that they might be delivered from their sin. From the beginning the Church has honored the memory of the dead and offered prayers in suffrage for them, above all the Eucharistic sacrifice, so that, thus purified, they may attain the beatific vision of God. The Church also commends almsgiving, indulgences, and works of penance undertaken on behalf of the dead...