Nematic liquid crystals can switch the orientation of the director under influence of an electric field. Liquid crystals can
be combined with waveguides in many different ways: the liquid crystal can be in the core, in the cladding or in both. In
the recent past liquid crystals have been combined with glass fibers and with silicon-on-insulator waveguides. Important
progress has been achieved in the modeling of liquid crystals near inhomogeneous boundaries and the modeling of
optical waveguides with anisotropic materials. This paper discusses these recent advancements and illustrates how
waveguides with voltage tuned cutoff may be designed.