The lattice Boltzmann model has evolved from the lattice gas model. In this chapter we outline the changes which have been made to the lattice gas formulation in order to overcome the problems associated with it. The accumulation of these alterations has resulted in the lattice Boltzmann model. This is described in detail for a single species fluid and it is shown that the correct form of the equilibrium distribution will ensure that the model is isotropic and Galilean invariant. Multi-fluid models are also considered with particular attention to the immiscible, binary fluid model of Orlandini et al. [9]. At the end of the chapter a number of simulation results using the Orlandini model are shown. These repeat results already presented [9, 38] and act to demonstrate some important features of the model and to test the model implementation.