Catholic Note:

Purgatory refers to a temporary state of purification for those who have died in the state of grace but still need to get rid of any lingering imperfections (venial sins, earthly attachments, self-will, etc.) before entering the perfection of Heaven.

 

Purgatory is like the Spiritual Hospital of Heaven.

Purgatory has NOTHING to do with ones justification or salvation. Those in Purgatory are justified; they are saved. Purgatory has to do with ones HOLINESS and the burning away of remaining self-love. Revelation 21:27

It's true that the word "Purgatory" doesn't appear in the Bible (neither do the words "Trinity", "Incarnation", "Altar Call" or even "Bible"). However, what's important is not the word, but the doctrine. And the doctrine of the final purification of the elect, apart from Heaven or Hell, is clearly taught in both the Old Testament and the New Testament."

 

If you are a Catholic interested in how to explain Purgatory to a Protestant, check out our Objections answered about Purgatory page.

 

Old Testament

 

If you are looking for Scriptural support you'll find it in the Second book of Maccabees among other places.

39 And the day following Judas cam with his company, to take away the bodies of them that were slain, and to bury them with their kinsmen, in the sepulchres of their fathers. 40 And they found under the coats o the slain some of the donaries of the idols of Jamnia, which the law had forbidden the Jews: 41 Then they all blessed the just judgment of the Lord, who had discovered the things that were hidden. 42 And so betaking themselves to prayers, they besought him, that the sin which had been committed might be forgotten. But the most valiant Judas exhorted the people to keep themselves from sin, forasmuch as they saw before their eyes what had happened, because of the sins of those that were slain. 43 And making a gathering, he twelve thousand drachms of silver to Jerusalem for sacrifice to be offered for the sins of the dead, thinking well and religiously concerning the resurrection, 44 (For if he had not hoped that the that were slain should rise again, it would have seemed superfluous and vain to pray for the dead,) 45 And because he considered that the who had fallen asleep with godliness, had great grace laid up for them. 46 It is therefore a holy and wholesome thought to pray for the dead, that they may be loosed from sins.

2 Maccabees 12:39-46

Side note: Though this book was rejected by the Protestant reformers and therefore is not in Protestant Bibles, one can not ignore the historical reality of this event and the reality of the words which were said.

Other Scriptural Support for Purgatory:

2 Samuel 12:13-14

David, though forgiven, is still punished for sin.

Matthew 5:25-26

"You will be thrown into prison and not be released until you have paid the last penny."

Matthew 5:48

"Be perfect as your Heavenly Father is perfect."
Perfection is to be strived for on earth.

Matthew 12:32

Sin against the Holy Spirit will not be forgiven, in this age, or the next.

Matthew 12:36

You will have to account for every idle word on judgment day.

1 Corinthians 3:10-16

"If someone's work is burned ... the person will be saved, but only as through fire."

1 Corinthians 15:29-30

Paul mentions people baptizing for the dead.

2 Timothy 1:16-18

St. Paul [prays/asks] that God have mercy on his dead friend, Onesiphorus.

Hebrews 12:14

Strive for that holiness without which one cannot see God.

Hebrews 12:29

For our God is a consuming fire.

James 1:14-15

When sin reaches maturity it reaches death.

James 3:2

We all fall short in many respects.

1 Peter 3:18-20 — 1 Peter 4:6

Jesus preached to the spirits in prison.

1 John 5:16-17

Distinction made between deadly sins and one that are not deadly.

Revelation 21:27

Nothing unclean will be allowed to enter into Heaven.

See Also:

Leviticus 26:41-43; Isaiah 4:4, Isaiah 6:5-7, Isaiah 33:11-14, Micah 7:8-9, Zechariah 9:11, Malachi 3:2-4, Matthew 18:34ff, Luke 12:58ff,
Luke 16:19-31, 2 Corinthians 5:10, 2 Corinthians 7:1, Ephesians 4:8-10, Philippians 2:10-11, 1 Peter 4:6, Revelation 5:3, 13

Also prayer for the dead is an ancient Jewish Tradition which is still carried out to this day.