The study of the habitable conditions in the outer solar system tends to enlarge the limits of the traditional habitable zone.Several of the icy moons show such promising conditions for the development and/or maintenance of life.Jupiters Europa, Callisto and Ganymede as well as Saturns Titan and Enceladus, seem to satisft many of the "classical" criteria for habitability such as the presence of liquid water, the energy sources to sustain metabolism and the "nutrients" over a period of time long enough to allow the development of life.