For crystalline porous materials, and for materials of large surface area in general, adsorption of gas and condensation in pores play an important role. First, these phenomena provide an excellent method for the characterisation of the surface area, the pore structure and pore volume of these materials, which are important in catalysis, gas separation, hydrogen storage, and in energy applications. Second, porous materials have interesting fundamental aspects. The phase transitions are shifted so that the condensation temperature of wettable surfaces is higher in pores but the freezing point is lower than in the bulk. The proximity of the surface can induce layering transitions, and new phases with new critical points emerge. The dynamics of molecules trapped in pores is often reduced, but it may also be enhanced compared with the liquid state when confinement in pores reduces the option to form hydrogen bonds.