So far, we have concentrated only on statistical and geometrical properties of percolation clusters. As we indicated in the introduction, many applications of the theory concern other properties, which arise by superimposing some additional processes which occur on top of the dilute sample. Examples included the propagation of forest fires, the flow of fluid in a porous medium and the diffusion of particles through a dilute system. The remaining chapters of this book aim to review some of these applications more quantitatively.