The use of optical excitation of guided modes to study the director profile in thin liquid crystal layers is well established. The most commonly used coupling geometry is that of prism-coupling, the prism providing the required extra in-plane momentum to allow coupling between the external radiation and the guided modes in the liquid crystal layer. A second coupling arrangement involves the use of a grating to provide the extra in-plane momentum by diffraction. Optical modelling of grating structures with liquid crystal layers is by no means as easy as modelling the planar prism-coupled system. In this article we examine both experiments involved with, and the theoretical modelling of, grating coupling to guided modes in liquid crystals.