"When most mortals have lived their allotted time, their spirits move on to whatever realm their destiny (or fate) sends them. They do not question this process, nor do they fight it. There are others, however, who do not go so gentle into that good night, bright light, or blazing inferno. They manage to not let something as trivial as their death keep them from hanging around and being a part of life on Earth. Call them spooks, spirits, poltergeists, phantoms, or just good old ghosts, there's one thing every player in the ultimate battle for the soul of Mankind knows: Ignore them at your own risk.
Liber Umbrarum expands greatly on the rules for ghosts first touched on in the Corporeal Player's Guide for In Nomine, with details on a dozen new types of ghosts, ideas for ghost-centered campaigns, ghosts as player-characters, allowing a slain PC to remain in the game as a ghost, new advantages and disadvantages for dealing with ghosts, and more."