As was mentioned in Chap. 1, all conservation equations have similar structure and may be regarded as special cases of a generic transport equation, Eq. (1.26), (1.27) or (1.28). For this reason, we shall treat only a single, generic conservation equation in this and the following chapters. It will be used to demonstrate discretization methods for the terms which are common to all conservation equations (convection, diffusion, and sources). The special features of the Navier-Stokes equations, and techniques for solving coupled non-linear problems will be introduced later. Also, for the time being, the unsteady term will be dropped so we shall consider only time-independent problems.