The only coherent mathematical theory describing the propagation of optical
beams in nematic liquid crystals under actual experimental conditions has been developed. This theory was then used to study the interaction and control of nonlinear optical beams in nematic liquid crystals under a wide range of experimental conditions. Most proposed applications of optical beams in liquid crystals are based on their control, particularly the control of their trajectories. The theory has been shown to be in excellent agreement with experimental and numerical results under a wide range of conditions. In particular, it has also been shown to be valid for liquid crystals which are doped with dyes or nano-particles. Such doping enhances the control mechanisms for the beams and also improves the properties of the liquid crystals.