The introduction of a body force into the lattice Boltzmann scheme has been studied. A number of techniques have been examined and a new method proposed which introduces a body force directly into the Boltzmann equation. The new method has been shown to act in a very similar way to an existing method and has been seen to have the expected effect on the fluid. The new method has been seen to be equally applicable to a single species and a two species fluid. The introduction of the body force has been shown to be independent of the orientation of the lattice and has been shown to preserve the Galilean invariance of the lattice Boltzmann model.