The number of the Beast, 666, is associated with the mark of the Beast and the name of the Beast in Revelation 13:17. We are told to "count the number" and that it is "the number of a man" (Revelation 13:18). One early explanation is attributed to John's disciple Polycarp, who, according to his student Irenaeus, said this number is derived from adding together the numerical equivalents of the letters in the word Lateinos, the Greek word for "Roman"—this being the name of the Beast empire, its ruler and everyone in it. So the number may well denote this general distinction, though it could also be more specific.

Another explanation is that the Bible associates the number six with man; God made him on the sixth day of creation week. The number 666 is a triple repetition of the number of man and emphasizes that this beast represents a government whose base is human authority, as opposed to God's authority.

As with the mark of the Beast, God's people will reject it. They will "have the victory over the beast, over his image and over his mark and over the number of his name" (Revelation 15:2). However this prophecy is fulfilled, it is clear that accepting the mark or number will involve compromising and contradicting God's commands. Having proof that one is officially associated in some way with the Beast will be necessary for one to be allowed to engage in commerce (Revelation 13:17).

Exactly how the end-time number of the Beast, 666, will be used and applied is not yet clear. But in some way it will be associated with the Beast's name and applied to his evil activities.