There is an urgent need for a complete model of concrete systems. One of the most important properties is the transport of moisture into and out of the microstructure and the transport of aggressive chemicals into and through this structure. Although the need is great, present models are incomplete. However, various strategies have been defined and important partial models have been developed. Both computer-based models and mathematical expressions describe transport and deterioration processes. Computer models account for the spatial distribution of phases, but encounter problems of scale, while mathematical expressions are unable to account explicitly for the spatial distribution of phases. Since such properties as permeability depend on the connectivity of pores (i.e. the shape and spatial distribution of pores) in addition to the volume fraction, microstructural models must be developed further. Nevertheless, the 30 contributions to this book present the most up-to-date summary of knowledge about concrete systems and their modelling, covering the scale and resolution of models; spatial distributions; databases and expert systems; transport mechanisms and the major parameters affecting them; and corrosion mechanisms and parameters.