The mechanisms of water transport are then addressed. In particular, classical water vapor diffusion is discussed in detail, including the conditions for dew formation, as well as the transport of liquid water in unsaturated pore spaces. The other transport mechanisms are briefly described, but sufficiently to facilitate understanding. Following this, the Glaser method is described in terms of its practical implementation, climatic boundary conditions, and application limits, with examples provided for clarification. Finally, recent unsteady-state calculation methods for moisture distribution in layered building materials are discussed. After a brief excursion into the field of solution diffusion, which primarily applies to organic polymers and less to porous mineral building materials, a final, relatively detailed section is presented.