A Penal World is a class of Imperial world that functions as a world-wide military-prison planet. A single such world's population consists entirely of criminals from hundreds of different worlds. This type of worlds tends to be barren worlds that have few other uses and have little, if any, indigenous population. Military formations are often raised from amongst the prison population as necessary, to serve as Penal Legion troops within Imperial Guard regiments. There, they might earn redemption through their term of service, which is for life.