Millennium is a Latin term meaning "thousand years".

The Old Testament speaks often of the Age to Come, in which a New Covenant would be made between God and man, and God's Spirit would live in men's hearts. (Jer. 31:31-34; Ezek. 36:25-27). Messiah is to reign then (Dan. 7:13-14).

In the New Testament, Revelation chapter 20 speaks of Satan being bound for "a thousand years", then loosed afterwards. At the beginning of this thousand years, the righteous dead are raised and reign with Christ. The rest of the dead are raised at the end of the 1000 years.

Several approaches are taken to the details. Amillennialism ("no millennium") comes in two major forms. Both regard the 1000 years as representative of some long period of time, just as God's ownership of "the cattle on a thousand hills" (Psalm 50:10) is not limited to a literal 1000 hills. One form sees the Millennium as present now, with Christ reigning in the hearts of those who are saved. Christians have passed from death to life (Jn. 5:24), and are seated with Christ in heavenly places (Eph. 2:6). This form may or may not expect a literal physical return of Jesus Christ. The second form sees the Millenium as symbolic of the entire Age to Come (Eternity) after Christ returns. The "first resurrection" in Rev. 20 is the spiritual resurrection of believers, with a physical resurrection of all when Christ returns, with judgment and spiritual death the fate of unbelievers at that point.

The Postmillennial view ("after the millennium") includes much in common with Amillenialism, but especially emphasizes that God means the Gospel to be successful in bringing people to Him and transforming their lives, and through them, society. At some point, earth will be actually to a large degree acknowledging Christ as Lord. In this Millennium, Christ rules through the Gospel, and physically returns sometime after this rule has been established.

Premillennialism ("before the millennium") sees Christ physically returning to set up His Kingdom. Christians are physically raised at that point, while unbelievers are not raised until 1000 years later. It sees the Millenium as separate both from the current age and from the Eternal Age to Come. There are various subdivisions within this view, with one of the major differences being whether Christians are caught up to be with the Lord before or after a time of great persecution. Along with this is the question whether Old Testament believers, such as Abraham, Moses, and David, are physically raised along with Christians before the millennium, or raised at the end of the millennium. The theological difference revolves around whether Old Testament and New Testament believers are all seen as one people of God, all saved by faith in God's provision, or whether Old Testament believers are a separate people of God from the Church.