H2O is a substance that only on the Earth exists in three phases: solid, liquid and gaseous. On other celestial bodies known to us it does not occur in a tri-phase state. An analysis of the definitions of water, ice, hydrosphere and the kryosphere shows that in this context they lack cohesion. Alongside ice, with its varied material forms in nature, another constituent of the kryosphere is temperature. Those two elements create the kryosphere. Their characterisation in consequence is the characterisation of ice and permafrost presented in the aforementioned context. This book discusses the kryosphere in detail, including its relationship with the hydrosphere.