The Deus Ex Bible is a collection of design documents the Deus Ex developers compiled and used to craft Deus Ex and also contains numerous Q&A sessions between Planet Deus Ex and the developers. It contains two parts.
The Deus Ex Bible is intended to summarize the universe details behind the Deus Ex universe with a few additions and modifications for the sake of maintaining consistency with the finished game and the current Deus Ex universe.
Although some things didn't appear in Deus Ex (many missions in Texas, moon base etc.) and shouldn't be considered canon, the Bible looks closely at the details and background behind the events that appeared in the finished game.